Problem p02937 (C++)

Buggy submission (status: Runtime Error):
const int mod1 = 1000000007, mod2 = 998244353;
const int mod = mod1;
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;
// Andrew He's modular-arithmetic class
template <int MOD_> struct modnum {
  static constexpr int MOD = MOD_;
  static_assert(MOD_ > 0, "MOD must be positive");

private:
  using ll = long long;

  int v;

  static int minv(int a, int m) {
    a %= m;
    assert(a);
    return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
  }

public:
  modnum() : v(0) {}
  modnum(ll v_) : v(int(v_ % MOD)) {
    if (v < 0)
      v += MOD;
  }
  explicit operator int() const { return v; }
  friend std::ostream &operator<<(std::ostream &out, const modnum &n) {
    return out << int(n);
  }
  friend std::istream &operator>>(std::istream &in, modnum &n) {
    ll v_;
    in >> v_;
    n = modnum(v_);
    return in;
  }

  friend bool operator==(const modnum &a, const modnum &b) {
    return a.v == b.v;
  }
  friend bool operator!=(const modnum &a, const modnum &b) {
    return a.v != b.v;
  }

  modnum inv() const {
    modnum res;
    res.v = minv(v, MOD);
    return res;
  }
  modnum neg() const {
    modnum res;
    res.v = v ? MOD - v : 0;
    return res;
  }
  modnum operator-() const { return neg(); }
  modnum operator+() const { return modnum(*this); }

  modnum &operator++() {
    v++;
    if (v == MOD)
      v = 0;
    return *this;
  }
  modnum &operator--() {
    if (v == 0)
      v = MOD;
    v--;
    return *this;
  }
  modnum &operator+=(const modnum &o) {
    v += o.v;
    if (v >= MOD)
      v -= MOD;
    return *this;
  }
  modnum &operator-=(const modnum &o) {
    v -= o.v;
    if (v < 0)
      v += MOD;
    return *this;
  }
  modnum &operator*=(const modnum &o) {
    v = int(ll(v) * ll(o.v) % MOD);
    return *this;
  }
  modnum &operator/=(const modnum &o) { return *this *= o.inv(); }

  friend modnum operator++(modnum &a, int) {
    modnum r = a;
    ++a;
    return r;
  }
  friend modnum operator--(modnum &a, int) {
    modnum r = a;
    --a;
    return r;
  }
  friend modnum operator+(const modnum &a, const modnum &b) {
    return modnum(a) += b;
  }
  friend modnum operator-(const modnum &a, const modnum &b) {
    return modnum(a) -= b;
  }
  friend modnum operator*(const modnum &a, const modnum &b) {
    return modnum(a) *= b;
  }
  friend modnum operator/(const modnum &a, const modnum &b) {
    return modnum(a) /= b;
  }
  friend modnum pow(modnum x, size_t n) {
    modnum res = 1;
    while (n) {
      if (n & 1)
        res *= x;
      x *= x;
      n /= 2;
    }
    return res;
  }
};

struct Modnum {
private:
  static int MOD; // declaration, not definition
  using ll = long long;
  using modnum = Modnum;
  int v;

  static int minv(int a, int m) {
    a %= m;
    assert(a);
    return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
  }

public:
  Modnum() : v(0) {}
  Modnum(ll v_) : v(int(v_ % MOD)) {
    if (v < 0)
      v += MOD;
  }
  static void set_mod(const int &m) {
    assert(m > 0);
    MOD = m;
  }
  explicit operator int() const { return v; }
  friend std::ostream &operator<<(std::ostream &out, const modnum &n) {
    return out << int(n);
  }
  friend std::istream &operator>>(std::istream &in, modnum &n) {
    ll v_;
    in >> v_;
    n = modnum(v_);
    return in;
  }

  friend bool operator==(const modnum &a, const modnum &b) {
    return a.v == b.v;
  }
  friend bool operator!=(const modnum &a, const modnum &b) {
    return a.v != b.v;
  }

  modnum inv() const {
    modnum res;
    res.v = minv(v, MOD);
    return res;
  }
  modnum neg() const {
    modnum res;
    res.v = v ? MOD - v : 0;
    return res;
  }
  modnum operator-() const { return neg(); }
  modnum operator+() const { return *this; }

  modnum &operator++() {
    v++;
    if (v == MOD)
      v = 0;
    return *this;
  }
  modnum &operator--() {
    if (v == 0)
      v = MOD;
    v--;
    return *this;
  }
  modnum &operator+=(const modnum &o) {
    v += o.v;
    if (v >= MOD)
      v -= MOD;
    return *this;
  }
  modnum &operator-=(const modnum &o) {
    v -= o.v;
    if (v < 0)
      v += MOD;
    return *this;
  }
  modnum &operator*=(const modnum &o) {
    v = int(ll(v) * ll(o.v) % MOD);
    return *this;
  }
  modnum &operator/=(const modnum &o) { return *this *= o.inv(); }

  friend modnum operator++(modnum &a, int) {
    modnum r = a;
    ++a;
    return r;
  }
  friend modnum operator--(modnum &a, int) {
    modnum r = a;
    --a;
    return r;
  }
  friend modnum operator+(const modnum &a, const modnum &b) {
    return modnum(a) += b;
  }
  friend modnum operator-(const modnum &a, const modnum &b) {
    return modnum(a) -= b;
  }
  friend modnum operator*(const modnum &a, const modnum &b) {
    return modnum(a) *= b;
  }
  friend modnum operator/(const modnum &a, const modnum &b) {
    return modnum(a) /= b;
  }
};
int Modnum::MOD = 1; // definition

#define sq(x) (x) * (x) // square
#define FAST_READ                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(nullptr);
#ifdef LOCAL
#define see(x) cout << "<DBG> " << #x << ": " << (x) << endl
#endif
#ifndef LOCAL
#define see(x)
#endif
#define LSON(x) ((x)*2)
#define RSON(x) ((x)*2 + 1)
template <typename A, typename B> void Min(A &a, const B &b) {
  if (b < a)
    a = b;
}
template <typename A, typename B> void Max(A &a, const B &b) {
  if (b > a)
    a = b;
}

int cas;
ostream &kase() { return cout << "Case #" << ++cas << ": "; }

#if __cplusplus < 201402L
template <class Iterator>
std::reverse_iterator<Iterator> make_reverse_iterator(Iterator it) {
  return std::reverse_iterator<Iterator>(it);
}
#endif

template <typename iter_t> struct iter_pair {
  iter_t _beg, _end;
  iter_t begin() { return _beg; }
  iter_t end() { return _end; }
};

template <class cont>
iter_pair<reverse_iterator<decltype(begin(declval<cont>()))>>
reverse(cont &&r) {
  return {make_reverse_iterator(end(r)), make_reverse_iterator(begin(r))};
}

template <typename T> void dprintln(const T &t) {
  cout << t << endl;
} // for debug use
template <typename T, typename... Args>
void dprintln(const T &t, const Args &...rest) {
  cout << t << ' ';
  dprintln(rest...);
}
template <typename T> void println(const T &t) { cout << t << '\n'; }

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  cout << t << ' ';
  println(rest...);
}
template <typename T> void println(const vector<T> &vec) {
  if (!vec.empty()) {
    cout << vec[0];
    for (size_t i = 1; i < vec.size(); ++i)
      cout << ' ' << vec[i];
  }
  cout << endl;
}

template <typename T> void print(const T &t) { cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  cout << t << ' ';
  print(rest...);
}

// this overload is chosen when there's only one argument
template <class T> void scan(T &t) { cin >> t; }
template <class T, class... Args> void scan(T &a, Args &...rest) {
  cin >> a;
  scan(rest...);
}
template <typename T> void scan(vector<T> &vec) {
  for (T &x : vec)
    scan(x);
}
using ull = unsigned long long;
using ll = long long;
using ul = unsigned long;
using vl = vector<ll>;
using vi = vector<int>;
using pii = pair<int, int>;
using pip = pair<int, pii>;
using pll = pair<ll, ll>;
using vb = vector<bool>;
using vpii = vector<pii>;
using ldb = long double;
template <typename int_t> inline int_t lowbit(int_t x) { return x & -x; }
#define rng(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define up(i, a, b) for (int i = int(a); i <= int(b); ++i)
#define down(i, b, a) for (int i = int(b); i >= int(a); i--)
#define rep(n) for (int i##n = 0, _##n = (int)n; i##n < _##n; i##n++)
#define stp(i, a, b, c) for (int i = (a); i < (b); i += (c))
#define FOR(x, cont) for (const auto &x : cont)
#define INC(init, x, y) for (init; x <= y; ++x)
#define For(x, cont) for (auto &x : cont)
#define all(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define SZ(x) (int)(x).size()
#define UP(i, l, r) for (i = decltype(i)(l); i <= decltype(i)(r); ++i)
#define DOWN(i, r, l) for (i = decltype(i)(r); i >= decltype(i)(l); --i)
#define Dec(a, b) for (; a >= b; --a)
template <typename T, typename Comp = less<T>>
using pq = priority_queue<T, vector<T>, Comp>;
#define popcnt(x) __builtin_popcountll((x))
#define SET(arr, v) memset(arr, (v), sizeof(arr))
#define UNIQ(vec) (vec).erase(unique(all(vec)), end(vec))
#define LB(cont, x) int(lower_bound(all(cont), x) - begin(cont))
#define UB(cont, x) int(upper_bound(all(cont), x) - begin(cont))
#define AI(name, n, m) vv<int> name(n, vi(m));
#define AL(name, n, m) vv<ll> name(size_t(n), vl(size_t(m)));
#define set0(arr) memset(arr, 0, sizeof arr)
#define set1(arr) memset(arr, -1, sizeof arr)
#define AT(T, n, m, a) vector<vector<T>> a(n, vector<T>(m))
const int dx[] = {0, 0, -1, 1}, dy[] = {-1, 1, 0, 0};
auto bet = [](const ll x, const ll y, const ll i) { return x <= i && i <= y; };

template <typename T1, typename T2>
T1 ceil(T1 x, T2 y) { // y >= 1，是整数。需要注意 x + y - 1 是否会溢出
  return (x + y - 1) / y;
}

inline int h_bit(unsigned long long x) {
  return sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(x);
}

int pow2(int x) { // power of 2
  return 1 << (h_bit((ull)x) + (x != lowbit(x)));
}

template <typename T> struct bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  const T init;
  explicit bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(bin_op), init(init) {
    a.assign(n + 1, init);
  }

  T prefix(T x) {
    auto res = init;
    while (x) {
      res = bin_op(a[x], res);
      x -= x & -x;
    }
    return res;
  }
  void modify(int x, T v) {
    while (x < (int)a.size()) {
      a[x] = bin_op(a[x], v);
      x += x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), init); }
};

template <typename T> struct r_bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  const T init;
  explicit r_bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(move(bin_op)), init(init) {
    a.ssign(n + 1, init);
  }
  T suffix(int x) {
    T res = init;
    while (x < SZ(a)) {
      res = bin_op(res, a[x]);
      x += x & -x;
    }
    return res;
  }
  void modify(int x, T v) {
    while (x > 0) {
      a[x] = bin_op(a[x], v);
      x -= x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), init); }
};

vi get_prime(int n) {
  vi minp((ul)n + 1), p;
  for (int i = 2; i <= n; i++) {
    if (!minp[i]) {
      minp[i] = i;
      p.pb(i);
    }
    FOR(x, p) {
      if (x <= minp[i] && x * i <= n)
        minp[x * i] = x;
      else
        break;
    }
  }
  return p;
}

// alias templates
template <typename T> using vv = vector<vector<T>>;
template <typename T1, typename T2 = T1> using vp = vector<pair<T1, T2>>;
template <typename T, int n> using va = vector<array<T, n>>;

// order_of_key (k) : Number of items strictly smaller than k .
// find_by_order(k) : K-th element in a set (counting from zero).
#ifdef __GNUC__
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename T>
using rank_tree =
    __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                     __gnu_pbds::tree_order_statistics_node_update>;
#endif

// union-find 并查集
struct UF {
  vi par, sz;
  int n_tree;
  explicit UF(int n) { // 0-indexed
    par.assign(n, 0);
    sz.assign(n, 1);
    rng(i, 0, n) par[i] = i;
    n_tree = n;
  }
  int n_cluster() const { return n_tree; }
  int size(int x) { return sz[root(x)]; }
  int root(int x) { return x == par[x] ? x : par[x] = root(par[x]); }
  bool unite(int x, int y) {
    int rx = root(x), ry = root(y);
    if (rx != ry) {
      par[rx] = ry;
      --n_tree;
      sz[ry] += sz[rx];
      return true;
    }
    return false;
  }
};

template <typename T, typename Compare = std::less<T>> struct SparseTable {
  size_t n{}; // 0-indexed
  vv<T> a;

  template <typename ptr_t> SparseTable(ptr_t beg, ptr_t end) : n(end - beg) {
    a.resize((size_t)h_bit(n) + 1); // 注意：不能写成 h_bit(n)
    a[0].assign(beg, end);
    rng(i, 0, SZ(a) - 1) {
      a[i + 1].resize(n);
      rng(j, 0, n - (1u << i)) {
        a[i + 1][j] = min(a[i][j], a[i][j + (1u << i)], Compare());
      }
      rng(j, n - (1u << i), n) { a[i + 1][j] = a[i][j]; }
    }
  }
  using idx_t = long;
  T query(idx_t l, idx_t r) { // l <=  r
    int i = h_bit(r - l + 1ul);
    return min(a[i][l], a[i][r + 1 - (1u << i)], Compare());
  }
};

vi get_popcnt(int n) {
  vi res((ul)n + 1);
  rng(i, 0, n) {
    if (i * 2 <= n)
      res[i * 2] = res[i];
    if ((i & 1) == 0)
      res[i + 1] = res[i] + 1;
  }
  return res;
}

vi get_mu(int n) {
  assert(n > 0);
  vi mu(n + 1);
  vi min_p(n + 1);
  vi prime;
  mu[1] = 1;
  rng(i, 2, n + 1) {
    if (!min_p[i]) {
      prime.pb(i);
      min_p[i] = i;
      mu[i] = -1;
    }
    FOR(p, prime) {
      if (p > min_p[i]) {
        break;
      }
      int t = p * i;
      if (t > n)
        break;
      min_p[t] = p;
      mu[t] = p == min_p[i] ? 0 : -mu[i];
    }
  }
  return mu;
}

template <typename num> num fp(num x, ll n) { // fast power: hat off to quailty
  if (n < 0) {
    x = fp(x, mod - 2);
    n = -n;
  }
  num ans = 1;
  while (n) {
    if (n & 1)
      ans *= x;
    n /= 2;
    x *= x;
  }
  return ans;
}

template <typename num> void bit_reverse_swap(vector<num> &a) {
  int n = SZ(a);
  for (int i = 1, j = n >> 1, k; i < n - 1; i++) {
    if (i < j)
      swap(a[i], a[j]);
    // tricky
    for (k = n >> 1; j >= k; j -= k, k >>= 1)
      ; // inspect the highest "1"
    j += k;
  }
}

template <typename num> void FFT(vector<num> &a, int type) {
  bit_reverse_swap(a);
  int n = SZ(a);
  for (int i = 2; i <= n; i *= 2) {
    const auto wi = fp(3, type * (mod - 1) / i); // i次单位根
    for (int j = 0; j < n; j += i) {
      num w(1);
      for (int k = j, h = i >> 1; k < j + h; k++) {
        auto t = w * a[k + h], u = a[k];
        a[k] = u + t;
        a[k + h] = u - t;
        w *= wi;
      }
    }
  }
  const auto inv = num(n).inv();
  if (type == -1)
    for (auto &x : a)
      x *= inv;
}
template <typename num> void fp(vector<num> &a, const int n) {
  a.resize((ul)pow2((SZ(a) - 1) * n + 1));
  FFT(a, 1);
  for (auto &x : a)
    x = fp(x, n);
  FFT(a, -1);
}
// DEBUG code by tourist
string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// end DEBUG

// minimal geometry classes
struct point {
  int x, y;

  void read() { scan(x, y); }

  ll cross(const point &b) const { return 1LL * x * b.y - 1LL * y * b.x; }

  point operator-(const point &b) const { return {x - b.x, y - b.y}; }

  bool para(const point &b) const { // parallel
    return 1LL * x * b.y == 1LL * y * b.x;
  }

  bool operator<(const point &b) const { return cross(b) < 0; }
};

struct segment {
  point p, dir;

  bool on_same_line(const segment &other) const {
    return dir.para(other.dir) && (p - other.p).para(dir);
  }

  bool para(const segment &b) const { return dir.para(b.dir); }

  bool operator==(const segment &b) const { return this->on_same_line(b); }
};
struct fraction {
  int n, d;
  bool operator<(const fraction &that) const {
    return 1LL * n * that.d < 1LL * that.n * d;
  }
  bool operator==(const fraction &that) const {
    return n == that.n && d == that.d;
  }
  bool operator>=(const fraction &that) const { return !(*this < that); }
  bool operator>(const fraction &that) const {
    return 1LL * n * that.d > 1LL * that.n * d;
  }
  fraction inverse() const { return n < 0 ? fraction{-d, -n} : fraction{d, n}; }
  fraction(int n, int d) {
    if (d < 0)
      n = -n, d = -d;
    int g = __gcd(abs(n), d);
    n /= g, d /= g;
    this->n = n, this->d = d;
  }
  explicit fraction(int x) : n(x), d(1) {}
  fraction operator+(const fraction &that) const {
    return fraction{n * that.d + that.n * d, d * that.d};
  }
  fraction operator-(const fraction &that) const {
    return fraction{n * that.d - that.n * d, d * that.d};
  }
  fraction floor() const {
    if (d == 0)
      return *this;
    return fraction((n < 0 ? n - (d - 1) : n) / d);
  }
  friend ostream &operator<<(ostream &out, const fraction &f) {
    return out << "(" << f.n << ',' << f.d << ')';
  }
  pii to_pair() const { return {n, d}; }
};
using Num = modnum<mod>;
struct comb {
  vector<Num> f;
  explicit comb(int n) {
    f.resize(n + 1);
    f[0] = 1;
    up(i, 1, n) f[i] = f[i - 1] * i;
  }
  Num get(int x, int y) const {
    assert(x <= SZ(f) - 1);
    assert(x >= 0 && y >= 0);
    if (x < y)
      return 0;
    return f[x] / f[y] / f[x - y];
  }
};

// BEGIN 树剖模板
namespace HLD {
const int max_V = 1e5 + 5;
vi g[max_V]; // vertices are 1-indexed
int fa[max_V];
int sz[max_V];
int heavy_son[max_V];
int dep[max_V];

void dfs(int u, int f) {
  fa[u] = f;
  sz[u] = 1;
  dep[u] = dep[f] + 1;
  int hson = 0;
  FOR(v, g[u]) {
    if (v != f) {
      dfs(v, u);
      sz[u] += sz[v];
      if (sz[v] > sz[hson])
        hson = v;
    }
  }
  heavy_son[u] = hson;
}

int top[max_V];
int pos[max_V]; // 0-indexed

// https://codeforces.com/blog/entry/22072
void init(int n) { // 很好的写法！
  int idx = 0;
  rng(i, 1, n + 1) {
    if (i != heavy_son[fa[i]]) {
      for (int j = i; j != 0; j = heavy_son[j]) {
        top[j] = i;
        pos[j] = idx++;
      }
    }
  }
}

// 两种情况：1.修改路径上的边 2.修改路径上的点。
bool VALUE_ON_EDGE = true;

// BinOpr: binary operator
template <class BinOpr> void process_path(int u, int v, BinOpr op) {
  while (top[u] != top[v]) {
    if (dep[top[u]] < dep[top[v]])
      swap(u, v);
    op(pos[top[u]], pos[u]);
    u = fa[top[u]];
  }
  if (dep[u] > dep[v])
    swap(u, v);
  op(pos[u] + VALUE_ON_EDGE, pos[v]);
}
} // namespace HLD
// END 树剖模板
template <typename T> T get_mid(T l, T r) {
  assert(l <= r);
  return l + (r - l) / 2;
}
//////////////////^"^///////////////////////////////////

int main() {
  FAST_READ
  cout << fixed << setprecision(10);
#ifdef LOCAL
  ifstream in("main.in");
  cin.rdbuf(in.rdbuf());
//    ofstream out("main.out");
//    cout.rdbuf(out.rdbuf());
#endif

  string s, t;
  scan(s, t);
  vector<array<int, 26>> next(SZ(s));
  int n = SZ(s);
  fill(all(next.back()), n);
  next.back()[s.back() - 'a'] = n - 1;
  down(i, n - 2, 0) {
    next[i] = next[i + 1];
    next[i][s[i] - 'a'] = i;
  }
  rng(i, 1, n) {
    rng(j, 0, 26) {
      if (next[i][j] == n) {
        next[i][j] = next[0][j];
      }
    }
  }

  int pos = 0;
  ll ans = 0;
  FOR(x, t) {
    int tmp = next[pos][x - 'a'];
    if (tmp == n) {
      println(-1);
      return 0;
    }
    if (tmp < pos)
      ans += n;
    pos = tmp + 1;
  }
  println(ans + pos);

#ifdef LOCAL
  cout << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
  return 0;
}


Fixed submission:
const int mod1 = 1000000007, mod2 = 998244353;
const int mod = mod1;
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;
// Andrew He's modular-arithmetic class
template <int MOD_> struct modnum {
  static constexpr int MOD = MOD_;
  static_assert(MOD_ > 0, "MOD must be positive");

private:
  using ll = long long;

  int v;

  static int minv(int a, int m) {
    a %= m;
    assert(a);
    return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
  }

public:
  modnum() : v(0) {}
  modnum(ll v_) : v(int(v_ % MOD)) {
    if (v < 0)
      v += MOD;
  }
  explicit operator int() const { return v; }
  friend std::ostream &operator<<(std::ostream &out, const modnum &n) {
    return out << int(n);
  }
  friend std::istream &operator>>(std::istream &in, modnum &n) {
    ll v_;
    in >> v_;
    n = modnum(v_);
    return in;
  }

  friend bool operator==(const modnum &a, const modnum &b) {
    return a.v == b.v;
  }
  friend bool operator!=(const modnum &a, const modnum &b) {
    return a.v != b.v;
  }

  modnum inv() const {
    modnum res;
    res.v = minv(v, MOD);
    return res;
  }
  modnum neg() const {
    modnum res;
    res.v = v ? MOD - v : 0;
    return res;
  }
  modnum operator-() const { return neg(); }
  modnum operator+() const { return modnum(*this); }

  modnum &operator++() {
    v++;
    if (v == MOD)
      v = 0;
    return *this;
  }
  modnum &operator--() {
    if (v == 0)
      v = MOD;
    v--;
    return *this;
  }
  modnum &operator+=(const modnum &o) {
    v += o.v;
    if (v >= MOD)
      v -= MOD;
    return *this;
  }
  modnum &operator-=(const modnum &o) {
    v -= o.v;
    if (v < 0)
      v += MOD;
    return *this;
  }
  modnum &operator*=(const modnum &o) {
    v = int(ll(v) * ll(o.v) % MOD);
    return *this;
  }
  modnum &operator/=(const modnum &o) { return *this *= o.inv(); }

  friend modnum operator++(modnum &a, int) {
    modnum r = a;
    ++a;
    return r;
  }
  friend modnum operator--(modnum &a, int) {
    modnum r = a;
    --a;
    return r;
  }
  friend modnum operator+(const modnum &a, const modnum &b) {
    return modnum(a) += b;
  }
  friend modnum operator-(const modnum &a, const modnum &b) {
    return modnum(a) -= b;
  }
  friend modnum operator*(const modnum &a, const modnum &b) {
    return modnum(a) *= b;
  }
  friend modnum operator/(const modnum &a, const modnum &b) {
    return modnum(a) /= b;
  }
  friend modnum pow(modnum x, size_t n) {
    modnum res = 1;
    while (n) {
      if (n & 1)
        res *= x;
      x *= x;
      n /= 2;
    }
    return res;
  }
};

struct Modnum {
private:
  static int MOD; // declaration, not definition
  using ll = long long;
  using modnum = Modnum;
  int v;

  static int minv(int a, int m) {
    a %= m;
    assert(a);
    return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
  }

public:
  Modnum() : v(0) {}
  Modnum(ll v_) : v(int(v_ % MOD)) {
    if (v < 0)
      v += MOD;
  }
  static void set_mod(const int &m) {
    assert(m > 0);
    MOD = m;
  }
  explicit operator int() const { return v; }
  friend std::ostream &operator<<(std::ostream &out, const modnum &n) {
    return out << int(n);
  }
  friend std::istream &operator>>(std::istream &in, modnum &n) {
    ll v_;
    in >> v_;
    n = modnum(v_);
    return in;
  }

  friend bool operator==(const modnum &a, const modnum &b) {
    return a.v == b.v;
  }
  friend bool operator!=(const modnum &a, const modnum &b) {
    return a.v != b.v;
  }

  modnum inv() const {
    modnum res;
    res.v = minv(v, MOD);
    return res;
  }
  modnum neg() const {
    modnum res;
    res.v = v ? MOD - v : 0;
    return res;
  }
  modnum operator-() const { return neg(); }
  modnum operator+() const { return *this; }

  modnum &operator++() {
    v++;
    if (v == MOD)
      v = 0;
    return *this;
  }
  modnum &operator--() {
    if (v == 0)
      v = MOD;
    v--;
    return *this;
  }
  modnum &operator+=(const modnum &o) {
    v += o.v;
    if (v >= MOD)
      v -= MOD;
    return *this;
  }
  modnum &operator-=(const modnum &o) {
    v -= o.v;
    if (v < 0)
      v += MOD;
    return *this;
  }
  modnum &operator*=(const modnum &o) {
    v = int(ll(v) * ll(o.v) % MOD);
    return *this;
  }
  modnum &operator/=(const modnum &o) { return *this *= o.inv(); }

  friend modnum operator++(modnum &a, int) {
    modnum r = a;
    ++a;
    return r;
  }
  friend modnum operator--(modnum &a, int) {
    modnum r = a;
    --a;
    return r;
  }
  friend modnum operator+(const modnum &a, const modnum &b) {
    return modnum(a) += b;
  }
  friend modnum operator-(const modnum &a, const modnum &b) {
    return modnum(a) -= b;
  }
  friend modnum operator*(const modnum &a, const modnum &b) {
    return modnum(a) *= b;
  }
  friend modnum operator/(const modnum &a, const modnum &b) {
    return modnum(a) /= b;
  }
};
int Modnum::MOD = 1; // definition

#define sq(x) (x) * (x) // square
#define FAST_READ                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(nullptr);
#ifdef LOCAL
#define see(x) cout << "<DBG> " << #x << ": " << (x) << endl
#endif
#ifndef LOCAL
#define see(x)
#endif
#define LSON(x) ((x)*2)
#define RSON(x) ((x)*2 + 1)
template <typename A, typename B> void Min(A &a, const B &b) {
  if (b < a)
    a = b;
}
template <typename A, typename B> void Max(A &a, const B &b) {
  if (b > a)
    a = b;
}

int cas;
ostream &kase() { return cout << "Case #" << ++cas << ": "; }

#if __cplusplus < 201402L
template <class Iterator>
std::reverse_iterator<Iterator> make_reverse_iterator(Iterator it) {
  return std::reverse_iterator<Iterator>(it);
}
#endif

template <typename iter_t> struct iter_pair {
  iter_t _beg, _end;
  iter_t begin() { return _beg; }
  iter_t end() { return _end; }
};

template <class cont>
iter_pair<reverse_iterator<decltype(begin(declval<cont>()))>>
reverse(cont &&r) {
  return {make_reverse_iterator(end(r)), make_reverse_iterator(begin(r))};
}

template <typename T> void dprintln(const T &t) {
  cout << t << endl;
} // for debug use
template <typename T, typename... Args>
void dprintln(const T &t, const Args &...rest) {
  cout << t << ' ';
  dprintln(rest...);
}
template <typename T> void println(const T &t) { cout << t << '\n'; }

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  cout << t << ' ';
  println(rest...);
}
template <typename T> void println(const vector<T> &vec) {
  if (!vec.empty()) {
    cout << vec[0];
    for (size_t i = 1; i < vec.size(); ++i)
      cout << ' ' << vec[i];
  }
  cout << endl;
}

template <typename T> void print(const T &t) { cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  cout << t << ' ';
  print(rest...);
}

// this overload is chosen when there's only one argument
template <class T> void scan(T &t) { cin >> t; }
template <class T, class... Args> void scan(T &a, Args &...rest) {
  cin >> a;
  scan(rest...);
}
template <typename T> void scan(vector<T> &vec) {
  for (T &x : vec)
    scan(x);
}
using ull = unsigned long long;
using ll = long long;
using ul = unsigned long;
using vl = vector<ll>;
using vi = vector<int>;
using pii = pair<int, int>;
using pip = pair<int, pii>;
using pll = pair<ll, ll>;
using vb = vector<bool>;
using vpii = vector<pii>;
using ldb = long double;
template <typename int_t> inline int_t lowbit(int_t x) { return x & -x; }
#define rng(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define up(i, a, b) for (int i = int(a); i <= int(b); ++i)
#define down(i, b, a) for (int i = int(b); i >= int(a); i--)
#define rep(n) for (int i##n = 0, _##n = (int)n; i##n < _##n; i##n++)
#define stp(i, a, b, c) for (int i = (a); i < (b); i += (c))
#define FOR(x, cont) for (const auto &x : cont)
#define INC(init, x, y) for (init; x <= y; ++x)
#define For(x, cont) for (auto &x : cont)
#define all(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define SZ(x) (int)(x).size()
#define UP(i, l, r) for (i = decltype(i)(l); i <= decltype(i)(r); ++i)
#define DOWN(i, r, l) for (i = decltype(i)(r); i >= decltype(i)(l); --i)
#define Dec(a, b) for (; a >= b; --a)
template <typename T, typename Comp = less<T>>
using pq = priority_queue<T, vector<T>, Comp>;
#define popcnt(x) __builtin_popcountll((x))
#define SET(arr, v) memset(arr, (v), sizeof(arr))
#define UNIQ(vec) (vec).erase(unique(all(vec)), end(vec))
#define LB(cont, x) int(lower_bound(all(cont), x) - begin(cont))
#define UB(cont, x) int(upper_bound(all(cont), x) - begin(cont))
#define AI(name, n, m) vv<int> name(n, vi(m));
#define AL(name, n, m) vv<ll> name(size_t(n), vl(size_t(m)));
#define set0(arr) memset(arr, 0, sizeof arr)
#define set1(arr) memset(arr, -1, sizeof arr)
#define AT(T, n, m, a) vector<vector<T>> a(n, vector<T>(m))
const int dx[] = {0, 0, -1, 1}, dy[] = {-1, 1, 0, 0};
auto bet = [](const ll x, const ll y, const ll i) { return x <= i && i <= y; };

template <typename T1, typename T2>
T1 ceil(T1 x, T2 y) { // y >= 1，是整数。需要注意 x + y - 1 是否会溢出
  return (x + y - 1) / y;
}

inline int h_bit(unsigned long long x) {
  return sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(x);
}

int pow2(int x) { // power of 2
  return 1 << (h_bit((ull)x) + (x != lowbit(x)));
}

template <typename T> struct bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  const T init;
  explicit bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(bin_op), init(init) {
    a.assign(n + 1, init);
  }

  T prefix(T x) {
    auto res = init;
    while (x) {
      res = bin_op(a[x], res);
      x -= x & -x;
    }
    return res;
  }
  void modify(int x, T v) {
    while (x < (int)a.size()) {
      a[x] = bin_op(a[x], v);
      x += x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), init); }
};

template <typename T> struct r_bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  const T init;
  explicit r_bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(move(bin_op)), init(init) {
    a.ssign(n + 1, init);
  }
  T suffix(int x) {
    T res = init;
    while (x < SZ(a)) {
      res = bin_op(res, a[x]);
      x += x & -x;
    }
    return res;
  }
  void modify(int x, T v) {
    while (x > 0) {
      a[x] = bin_op(a[x], v);
      x -= x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), init); }
};

vi get_prime(int n) {
  vi minp((ul)n + 1), p;
  for (int i = 2; i <= n; i++) {
    if (!minp[i]) {
      minp[i] = i;
      p.pb(i);
    }
    FOR(x, p) {
      if (x <= minp[i] && x * i <= n)
        minp[x * i] = x;
      else
        break;
    }
  }
  return p;
}

// alias templates
template <typename T> using vv = vector<vector<T>>;
template <typename T1, typename T2 = T1> using vp = vector<pair<T1, T2>>;
template <typename T, int n> using va = vector<array<T, n>>;

// order_of_key (k) : Number of items strictly smaller than k .
// find_by_order(k) : K-th element in a set (counting from zero).
#ifdef __GNUC__
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename T>
using rank_tree =
    __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                     __gnu_pbds::tree_order_statistics_node_update>;
#endif

// union-find 并查集
struct UF {
  vi par, sz;
  int n_tree;
  explicit UF(int n) { // 0-indexed
    par.assign(n, 0);
    sz.assign(n, 1);
    rng(i, 0, n) par[i] = i;
    n_tree = n;
  }
  int n_cluster() const { return n_tree; }
  int size(int x) { return sz[root(x)]; }
  int root(int x) { return x == par[x] ? x : par[x] = root(par[x]); }
  bool unite(int x, int y) {
    int rx = root(x), ry = root(y);
    if (rx != ry) {
      par[rx] = ry;
      --n_tree;
      sz[ry] += sz[rx];
      return true;
    }
    return false;
  }
};

template <typename T, typename Compare = std::less<T>> struct SparseTable {
  size_t n{}; // 0-indexed
  vv<T> a;

  template <typename ptr_t> SparseTable(ptr_t beg, ptr_t end) : n(end - beg) {
    a.resize((size_t)h_bit(n) + 1); // 注意：不能写成 h_bit(n)
    a[0].assign(beg, end);
    rng(i, 0, SZ(a) - 1) {
      a[i + 1].resize(n);
      rng(j, 0, n - (1u << i)) {
        a[i + 1][j] = min(a[i][j], a[i][j + (1u << i)], Compare());
      }
      rng(j, n - (1u << i), n) { a[i + 1][j] = a[i][j]; }
    }
  }
  using idx_t = long;
  T query(idx_t l, idx_t r) { // l <=  r
    int i = h_bit(r - l + 1ul);
    return min(a[i][l], a[i][r + 1 - (1u << i)], Compare());
  }
};

vi get_popcnt(int n) {
  vi res((ul)n + 1);
  rng(i, 0, n) {
    if (i * 2 <= n)
      res[i * 2] = res[i];
    if ((i & 1) == 0)
      res[i + 1] = res[i] + 1;
  }
  return res;
}

vi get_mu(int n) {
  assert(n > 0);
  vi mu(n + 1);
  vi min_p(n + 1);
  vi prime;
  mu[1] = 1;
  rng(i, 2, n + 1) {
    if (!min_p[i]) {
      prime.pb(i);
      min_p[i] = i;
      mu[i] = -1;
    }
    FOR(p, prime) {
      if (p > min_p[i]) {
        break;
      }
      int t = p * i;
      if (t > n)
        break;
      min_p[t] = p;
      mu[t] = p == min_p[i] ? 0 : -mu[i];
    }
  }
  return mu;
}

template <typename num> num fp(num x, ll n) { // fast power: hat off to quailty
  if (n < 0) {
    x = fp(x, mod - 2);
    n = -n;
  }
  num ans = 1;
  while (n) {
    if (n & 1)
      ans *= x;
    n /= 2;
    x *= x;
  }
  return ans;
}

template <typename num> void bit_reverse_swap(vector<num> &a) {
  int n = SZ(a);
  for (int i = 1, j = n >> 1, k; i < n - 1; i++) {
    if (i < j)
      swap(a[i], a[j]);
    // tricky
    for (k = n >> 1; j >= k; j -= k, k >>= 1)
      ; // inspect the highest "1"
    j += k;
  }
}

template <typename num> void FFT(vector<num> &a, int type) {
  bit_reverse_swap(a);
  int n = SZ(a);
  for (int i = 2; i <= n; i *= 2) {
    const auto wi = fp(3, type * (mod - 1) / i); // i次单位根
    for (int j = 0; j < n; j += i) {
      num w(1);
      for (int k = j, h = i >> 1; k < j + h; k++) {
        auto t = w * a[k + h], u = a[k];
        a[k] = u + t;
        a[k + h] = u - t;
        w *= wi;
      }
    }
  }
  const auto inv = num(n).inv();
  if (type == -1)
    for (auto &x : a)
      x *= inv;
}
template <typename num> void fp(vector<num> &a, const int n) {
  a.resize((ul)pow2((SZ(a) - 1) * n + 1));
  FFT(a, 1);
  for (auto &x : a)
    x = fp(x, n);
  FFT(a, -1);
}
// DEBUG code by tourist
string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// end DEBUG

// minimal geometry classes
struct point {
  int x, y;

  void read() { scan(x, y); }

  ll cross(const point &b) const { return 1LL * x * b.y - 1LL * y * b.x; }

  point operator-(const point &b) const { return {x - b.x, y - b.y}; }

  bool para(const point &b) const { // parallel
    return 1LL * x * b.y == 1LL * y * b.x;
  }

  bool operator<(const point &b) const { return cross(b) < 0; }
};

struct segment {
  point p, dir;

  bool on_same_line(const segment &other) const {
    return dir.para(other.dir) && (p - other.p).para(dir);
  }

  bool para(const segment &b) const { return dir.para(b.dir); }

  bool operator==(const segment &b) const { return this->on_same_line(b); }
};
struct fraction {
  int n, d;
  bool operator<(const fraction &that) const {
    return 1LL * n * that.d < 1LL * that.n * d;
  }
  bool operator==(const fraction &that) const {
    return n == that.n && d == that.d;
  }
  bool operator>=(const fraction &that) const { return !(*this < that); }
  bool operator>(const fraction &that) const {
    return 1LL * n * that.d > 1LL * that.n * d;
  }
  fraction inverse() const { return n < 0 ? fraction{-d, -n} : fraction{d, n}; }
  fraction(int n, int d) {
    if (d < 0)
      n = -n, d = -d;
    int g = __gcd(abs(n), d);
    n /= g, d /= g;
    this->n = n, this->d = d;
  }
  explicit fraction(int x) : n(x), d(1) {}
  fraction operator+(const fraction &that) const {
    return fraction{n * that.d + that.n * d, d * that.d};
  }
  fraction operator-(const fraction &that) const {
    return fraction{n * that.d - that.n * d, d * that.d};
  }
  fraction floor() const {
    if (d == 0)
      return *this;
    return fraction((n < 0 ? n - (d - 1) : n) / d);
  }
  friend ostream &operator<<(ostream &out, const fraction &f) {
    return out << "(" << f.n << ',' << f.d << ')';
  }
  pii to_pair() const { return {n, d}; }
};
using Num = modnum<mod>;
struct comb {
  vector<Num> f;
  explicit comb(int n) {
    f.resize(n + 1);
    f[0] = 1;
    up(i, 1, n) f[i] = f[i - 1] * i;
  }
  Num get(int x, int y) const {
    assert(x <= SZ(f) - 1);
    assert(x >= 0 && y >= 0);
    if (x < y)
      return 0;
    return f[x] / f[y] / f[x - y];
  }
};

// BEGIN 树剖模板
namespace HLD {
const int max_V = 1e5 + 5;
vi g[max_V]; // vertices are 1-indexed
int fa[max_V];
int sz[max_V];
int heavy_son[max_V];
int dep[max_V];

void dfs(int u, int f) {
  fa[u] = f;
  sz[u] = 1;
  dep[u] = dep[f] + 1;
  int hson = 0;
  FOR(v, g[u]) {
    if (v != f) {
      dfs(v, u);
      sz[u] += sz[v];
      if (sz[v] > sz[hson])
        hson = v;
    }
  }
  heavy_son[u] = hson;
}

int top[max_V];
int pos[max_V]; // 0-indexed

// https://codeforces.com/blog/entry/22072
void init(int n) { // 很好的写法！
  int idx = 0;
  rng(i, 1, n + 1) {
    if (i != heavy_son[fa[i]]) {
      for (int j = i; j != 0; j = heavy_son[j]) {
        top[j] = i;
        pos[j] = idx++;
      }
    }
  }
}

// 两种情况：1.修改路径上的边 2.修改路径上的点。
bool VALUE_ON_EDGE = true;

// BinOpr: binary operator
template <class BinOpr> void process_path(int u, int v, BinOpr op) {
  while (top[u] != top[v]) {
    if (dep[top[u]] < dep[top[v]])
      swap(u, v);
    op(pos[top[u]], pos[u]);
    u = fa[top[u]];
  }
  if (dep[u] > dep[v])
    swap(u, v);
  op(pos[u] + VALUE_ON_EDGE, pos[v]);
}
} // namespace HLD
// END 树剖模板
template <typename T> T get_mid(T l, T r) {
  assert(l <= r);
  return l + (r - l) / 2;
}
//////////////////^"^///////////////////////////////////

int main() {
  FAST_READ
  cout << fixed << setprecision(10);
#ifdef LOCAL
  ifstream in("main.in");
  cin.rdbuf(in.rdbuf());
//    ofstream out("main.out");
//    cout.rdbuf(out.rdbuf());
#endif

  string s, t;
  scan(s, t);
  vector<array<int, 26>> next(SZ(s));
  int n = SZ(s);
  fill(all(next.back()), n);
  next.back()[s.back() - 'a'] = n - 1;
  down(i, n - 2, 0) {
    next[i] = next[i + 1];
    next[i][s[i] - 'a'] = i;
  }
  rng(i, 1, n) {
    rng(j, 0, 26) {
      if (next[i][j] == n) {
        next[i][j] = next[0][j];
      }
    }
  }

  int pos = 0;
  ll ans = 0;
  FOR(x, t) {
    int tmp = next[pos][x - 'a'];
    if (tmp == n) {
      println(-1);
      return 0;
    }
    if (tmp < pos)
      ans += n;
    pos = tmp + 1;
    if (pos == n) {
      ans += n;
      pos = 0;
    }
  }
  println(ans + pos);

#ifdef LOCAL
  cout << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
  return 0;
}