Problem p02632 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define ios std::ios::sync_with_stdio(false)
#define sd(n) scanf("%d", &n)
#define sdd(n, m) scanf("%d%d", &n, &m)
#define sddd(n, m, k) scanf("%d%d%d", &n, &m, &k)
#define pd(n) printf("%d\n", (n))
#define pdd(n, m) printf("%d %d\n", n, m)
#define pld(n) printf("%lld\n", n)
#define pldd(n, m) printf("%lld %lld\n", n, m)
#define sld(n) scanf("%lld", &n)
#define sldd(n, m) scanf("%lld%lld", &n, &m)
#define slddd(n, m, k) scanf("%lld%lld%lld", &n, &m, &k)
#define sf(n) scanf("%lf", &n)
#define sff(n, m) scanf("%lf%lf", &n, &m)
#define sfff(n, m, k) scanf("%lf%lf%lf", &n, &m, &k)
#define rep(i, a, n) for (int i = a; i <= n; i++)
#define per(i, n, a) for (int i = n; i >= a; i--)
#define mm(a, n) memset(a, n, sizeof(a))
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define il inline
#define int long long
#define ll long long
#define ull unsigned long long
#define MOD 1000000007
#define pi 3.14159265358979323
#define debug(x) cout << #x << ": " << x << endl;
#define debug2(x, y)                                                           \
  cout << #x << ": " << x << " | " << #y << ": " << y << endl;
#define debug3(x, y, z)                                                        \
  cout << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": "   \
       << z << endl;
#define debug4(a, b, c, d)                                                     \
  cout << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl;
using namespace std;
const ll INF(0x3f3f3f3f3f3f3f3fll);
const int inf(0x3f3f3f3f);
template <typename T> void read(T &res) {
  bool flag = false;
  char ch;
  while (!isdigit(ch = getchar()))
    (ch == '-') && (flag = true);
  for (res = ch - 48; isdigit(ch = getchar());
       res = (res << 1) + (res << 3) + ch - 48)
    ;
  flag && (res = -res);
}
template <typename T> void Out(T x) {
  if (x < 0)
    putchar('-'), x = -x;
  if (x > 9)
    Out(x / 10);
  putchar(x % 10 + '0');
}
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
ll pow_mod(ll x, ll n, ll mod) {
  ll res = 1;
  while (n) {
    if (n & 1)
      res = res * x % mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}
ll fact_pow(ll n, ll p) {
  ll res = 0;
  while (n) {
    n /= p;
    res += n;
  }
  return res;
}
ll mult(ll a, ll b, ll p) {
  a %= p;
  b %= p;
  ll r = 0, v = a;
  while (b) {
    if (b & 1) {
      r += v;
      if (r > p)
        r -= p;
    }
    v <<= 1;
    if (v > p)
      v -= p;
    b >>= 1;
  }
  return r;
}
ll quick_pow(ll a, ll b, ll p) {
  ll r = 1, v = a % p;
  while (b) {
    if (b & 1)
      r = mult(r, v, p);
    v = mult(v, v, p);
    b >>= 1;
  }
  return r;
}
bool CH(ll a, ll n, ll x, ll t) {
  ll r = quick_pow(a, x, n);
  ll z = r;
  for (ll i = 1; i <= t; i++) {
    r = mult(r, r, n);
    if (r == 1 && z != 1 && z != n - 1)
      return true;
    z = r;
  }
  return r != 1;
}
bool Miller_Rabin(ll n) {
  if (n < 2)
    return false;
  if (n == 2)
    return true;
  if (!(n & 1))
    return false;
  ll x = n - 1, t = 0;
  while (!(x & 1)) {
    x >>= 1;
    t++;
  }
  srand(time(NULL));
  ll o = 8;
  for (ll i = 0; i < o; i++) {
    ll a = rand() % (n - 1) + 1;
    if (CH(a, n, x, t))
      return false;
  }
  return true;
}
void exgcd(ll a, ll b, ll &x, ll &y) {
  if (!b) {
    x = 1, y = 0;
    return;
  }
  exgcd(b, a % b, x, y);
  ll t = x;
  x = y, y = t - (a / b) * y;
}
ll INV(ll a, ll b) {
  ll x, y;
  return exgcd(a, b, x, y), (x % b + b) % b;
}
ll crt(ll x, ll p, ll mod) { return INV(p / mod, mod) * (p / mod) * x; }
ll FAC(ll x, ll a, ll b) {
  if (!x)
    return 1;
  ll ans = 1;
  for (ll i = 1; i <= b; i++)
    if (i % a)
      ans *= i, ans %= b;
  ans = pow_mod(ans, x / b, b);
  for (ll i = 1; i <= x % b; i++)
    if (i % a)
      ans *= i, ans %= b;
  return ans * FAC(x / a, a, b) % b;
}
ll C(ll n, ll m, ll a, ll b) {
  ll N = FAC(n, a, b), M = FAC(m, a, b), Z = FAC(n - m, a, b), sum = 0, i;
  for (i = n; i; i = i / a)
    sum += i / a;
  for (i = m; i; i = i / a)
    sum -= i / a;
  for (i = n - m; i; i = i / a)
    sum -= i / a;
  return N * pow_mod(a, sum, b) % b * INV(M, b) % b * INV(Z, b) % b;
}
ll exlucas(ll n, ll m, ll p) {
  ll t = p, ans = 0, i;
  for (i = 2; i * i <= p; i++) {
    ll k = 1;
    while (t % i == 0) {
      k *= i, t /= i;
    }
    ans += crt(C(n, m, i, k), p, k), ans %= p;
  }
  if (t > 1)
    ans += crt(C(n, m, t, t), p, t), ans %= p;
  return ans % p;
}
/*
int prime[100000],minprime[100000];
int euler(int n)
{int
c=0,i,j;for(i=2;i<=n;i++){if(!minprime[i])prime[++c]=i,minprime[i]=i;for(j=1;j<=c&&i*prime[j]<=n;j++)
{minprime[i*prime[j]]=prime[j];if(i%prime[j]==0)break;}}return c;}
struct Tree{ll l,r,sum,lazy,maxn,minn;}tree[100000];
il void push_up(ll rt)
{tree[rt].sum=tree[rt<<1].sum+tree[rt<<1|1].sum;
tree[rt].maxn=max(tree[rt<<1].maxn,tree[rt<<1|1].maxn);
tree[rt].minn=min(tree[rt<<1].minn,tree[rt<<1|1].minn);}
il void push_down(ll rt , ll length)
{if(tree[rt].lazy){tree[rt<<1].lazy+=tree[rt].lazy;tree[rt<<1|1].lazy+=tree[rt].lazy;
tree[rt<<1].sum+=(length-(length>>1))*tree[rt].lazy;tree[rt<<1|1].sum+=(length>>1)*tree[rt].lazy;
tree[rt<<1].minn+=tree[rt].lazy;tree[rt<<1|1].minn+=tree[rt].lazy;
tree[rt<<1].maxn+=tree[rt].lazy;tree[rt<<1|1].maxn+=tree[rt].lazy;tree[rt].lazy=0;}}
il void build(ll l , ll r , ll rt , ll *aa)
{tree[rt].lazy=0;tree[rt].l=l;tree[rt].r=r;if(l==r)
{tree[rt].sum=aa[l];tree[rt].minn=tree[rt].sum;tree[rt].maxn=tree[rt].sum;return;}
ll mid=(l+r)>>1;build(l,mid,rt<<1,aa);build(mid+1,r,rt<<1|1,aa);push_up(rt);}
il void update_range(ll L , ll R , ll key , ll rt)
{if(tree[rt].r<L||tree[rt].l>R)return;if(L<=tree[rt].l&&R>=tree[rt].r){tree[rt].sum+=(tree[rt].r-tree[rt].l+1)*key;
tree[rt].minn+=key;tree[rt].maxn+=key;tree[rt].lazy+=key;return;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;if(L<=mid)update_range(L,R,key,rt << 1);
if(R>mid)update_range(L,R,key,rt << 1 | 1);push_up(rt);}
il ll query_range(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].sum;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll ans=0;if(L<=mid)ans+=query_range(L,R,rt << 1);
if(R>mid)ans+=query_range(L,R,rt << 1 | 1);return ans;}
il ll query_min(ll L,ll R,ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].minn;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll
ans=(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=min(ans,query_min(L,R,rt << 1));
if(R>mid)ans=min(ans,query_min(L,R,rt << 1 | 1));return ans;}
il ll query_max(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].maxn;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll
ans=-(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=max(ans,query_max(L,R,rt << 1));
if(R>mid)ans=max(ans,query_max(L,R,rt << 1 | 1));return ans;}
*/
const int N = 3e5 + 10;
struct Edge {
  int nex, to;
} edge[N << 1];
int head[N], tot;
void add_edge(int u, int v) {
  edge[++tot].nex = head[u];
  edge[tot].to = v;
  head[u] = tot;
}
int fac[N], inv[N];
void init() {
  fac[0] = 1;
  rep(i, 1, N - 10) fac[i] = fac[i - 1] * i % MOD;
  inv[N - 10] = pow_mod(fac[N - 10], MOD - 2, MOD);
  per(i, N - 11, 0) inv[i] = inv[i + 1] * (i + 1) % MOD;
}
int C(int n, int m) { return fac[n] * inv[n - m] % MOD * inv[m] % MOD; }
char s[N];
signed main() {
  ios;
  init();
  int k;
  cin >> k >> s + 1;
  int n = strlen(s + 1);
  int ans = 0;
  rep(i, 0, k) {
    ans += C(n + i - 1, n - 1) * pow_mod(25, i, MOD) % MOD *
           pow_mod(26, k - i, MOD) % MOD;
    ans %= MOD;
  }
  cout << ans << '\n';
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define ios std::ios::sync_with_stdio(false)
#define sd(n) scanf("%d", &n)
#define sdd(n, m) scanf("%d%d", &n, &m)
#define sddd(n, m, k) scanf("%d%d%d", &n, &m, &k)
#define pd(n) printf("%d\n", (n))
#define pdd(n, m) printf("%d %d\n", n, m)
#define pld(n) printf("%lld\n", n)
#define pldd(n, m) printf("%lld %lld\n", n, m)
#define sld(n) scanf("%lld", &n)
#define sldd(n, m) scanf("%lld%lld", &n, &m)
#define slddd(n, m, k) scanf("%lld%lld%lld", &n, &m, &k)
#define sf(n) scanf("%lf", &n)
#define sff(n, m) scanf("%lf%lf", &n, &m)
#define sfff(n, m, k) scanf("%lf%lf%lf", &n, &m, &k)
#define rep(i, a, n) for (int i = a; i <= n; i++)
#define per(i, n, a) for (int i = n; i >= a; i--)
#define mm(a, n) memset(a, n, sizeof(a))
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define il inline
#define int long long
#define ll long long
#define ull unsigned long long
#define MOD 1000000007
#define pi 3.14159265358979323
#define debug(x) cout << #x << ": " << x << endl;
#define debug2(x, y)                                                           \
  cout << #x << ": " << x << " | " << #y << ": " << y << endl;
#define debug3(x, y, z)                                                        \
  cout << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": "   \
       << z << endl;
#define debug4(a, b, c, d)                                                     \
  cout << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl;
using namespace std;
const ll INF(0x3f3f3f3f3f3f3f3fll);
const int inf(0x3f3f3f3f);
template <typename T> void read(T &res) {
  bool flag = false;
  char ch;
  while (!isdigit(ch = getchar()))
    (ch == '-') && (flag = true);
  for (res = ch - 48; isdigit(ch = getchar());
       res = (res << 1) + (res << 3) + ch - 48)
    ;
  flag && (res = -res);
}
template <typename T> void Out(T x) {
  if (x < 0)
    putchar('-'), x = -x;
  if (x > 9)
    Out(x / 10);
  putchar(x % 10 + '0');
}
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }
ll pow_mod(ll x, ll n, ll mod) {
  ll res = 1;
  while (n) {
    if (n & 1)
      res = res * x % mod;
    x = x * x % mod;
    n >>= 1;
  }
  return res;
}
ll fact_pow(ll n, ll p) {
  ll res = 0;
  while (n) {
    n /= p;
    res += n;
  }
  return res;
}
ll mult(ll a, ll b, ll p) {
  a %= p;
  b %= p;
  ll r = 0, v = a;
  while (b) {
    if (b & 1) {
      r += v;
      if (r > p)
        r -= p;
    }
    v <<= 1;
    if (v > p)
      v -= p;
    b >>= 1;
  }
  return r;
}
ll quick_pow(ll a, ll b, ll p) {
  ll r = 1, v = a % p;
  while (b) {
    if (b & 1)
      r = mult(r, v, p);
    v = mult(v, v, p);
    b >>= 1;
  }
  return r;
}
bool CH(ll a, ll n, ll x, ll t) {
  ll r = quick_pow(a, x, n);
  ll z = r;
  for (ll i = 1; i <= t; i++) {
    r = mult(r, r, n);
    if (r == 1 && z != 1 && z != n - 1)
      return true;
    z = r;
  }
  return r != 1;
}
bool Miller_Rabin(ll n) {
  if (n < 2)
    return false;
  if (n == 2)
    return true;
  if (!(n & 1))
    return false;
  ll x = n - 1, t = 0;
  while (!(x & 1)) {
    x >>= 1;
    t++;
  }
  srand(time(NULL));
  ll o = 8;
  for (ll i = 0; i < o; i++) {
    ll a = rand() % (n - 1) + 1;
    if (CH(a, n, x, t))
      return false;
  }
  return true;
}
void exgcd(ll a, ll b, ll &x, ll &y) {
  if (!b) {
    x = 1, y = 0;
    return;
  }
  exgcd(b, a % b, x, y);
  ll t = x;
  x = y, y = t - (a / b) * y;
}
ll INV(ll a, ll b) {
  ll x, y;
  return exgcd(a, b, x, y), (x % b + b) % b;
}
ll crt(ll x, ll p, ll mod) { return INV(p / mod, mod) * (p / mod) * x; }
ll FAC(ll x, ll a, ll b) {
  if (!x)
    return 1;
  ll ans = 1;
  for (ll i = 1; i <= b; i++)
    if (i % a)
      ans *= i, ans %= b;
  ans = pow_mod(ans, x / b, b);
  for (ll i = 1; i <= x % b; i++)
    if (i % a)
      ans *= i, ans %= b;
  return ans * FAC(x / a, a, b) % b;
}
ll C(ll n, ll m, ll a, ll b) {
  ll N = FAC(n, a, b), M = FAC(m, a, b), Z = FAC(n - m, a, b), sum = 0, i;
  for (i = n; i; i = i / a)
    sum += i / a;
  for (i = m; i; i = i / a)
    sum -= i / a;
  for (i = n - m; i; i = i / a)
    sum -= i / a;
  return N * pow_mod(a, sum, b) % b * INV(M, b) % b * INV(Z, b) % b;
}
ll exlucas(ll n, ll m, ll p) {
  ll t = p, ans = 0, i;
  for (i = 2; i * i <= p; i++) {
    ll k = 1;
    while (t % i == 0) {
      k *= i, t /= i;
    }
    ans += crt(C(n, m, i, k), p, k), ans %= p;
  }
  if (t > 1)
    ans += crt(C(n, m, t, t), p, t), ans %= p;
  return ans % p;
}
/*
int prime[100000],minprime[100000];
int euler(int n)
{int
c=0,i,j;for(i=2;i<=n;i++){if(!minprime[i])prime[++c]=i,minprime[i]=i;for(j=1;j<=c&&i*prime[j]<=n;j++)
{minprime[i*prime[j]]=prime[j];if(i%prime[j]==0)break;}}return c;}
struct Tree{ll l,r,sum,lazy,maxn,minn;}tree[100000];
il void push_up(ll rt)
{tree[rt].sum=tree[rt<<1].sum+tree[rt<<1|1].sum;
tree[rt].maxn=max(tree[rt<<1].maxn,tree[rt<<1|1].maxn);
tree[rt].minn=min(tree[rt<<1].minn,tree[rt<<1|1].minn);}
il void push_down(ll rt , ll length)
{if(tree[rt].lazy){tree[rt<<1].lazy+=tree[rt].lazy;tree[rt<<1|1].lazy+=tree[rt].lazy;
tree[rt<<1].sum+=(length-(length>>1))*tree[rt].lazy;tree[rt<<1|1].sum+=(length>>1)*tree[rt].lazy;
tree[rt<<1].minn+=tree[rt].lazy;tree[rt<<1|1].minn+=tree[rt].lazy;
tree[rt<<1].maxn+=tree[rt].lazy;tree[rt<<1|1].maxn+=tree[rt].lazy;tree[rt].lazy=0;}}
il void build(ll l , ll r , ll rt , ll *aa)
{tree[rt].lazy=0;tree[rt].l=l;tree[rt].r=r;if(l==r)
{tree[rt].sum=aa[l];tree[rt].minn=tree[rt].sum;tree[rt].maxn=tree[rt].sum;return;}
ll mid=(l+r)>>1;build(l,mid,rt<<1,aa);build(mid+1,r,rt<<1|1,aa);push_up(rt);}
il void update_range(ll L , ll R , ll key , ll rt)
{if(tree[rt].r<L||tree[rt].l>R)return;if(L<=tree[rt].l&&R>=tree[rt].r){tree[rt].sum+=(tree[rt].r-tree[rt].l+1)*key;
tree[rt].minn+=key;tree[rt].maxn+=key;tree[rt].lazy+=key;return;}push_down(rt,tree[rt].r-tree[rt].l+1);
ll mid=(tree[rt].r+tree[rt].l)>>1;if(L<=mid)update_range(L,R,key,rt << 1);
if(R>mid)update_range(L,R,key,rt << 1 | 1);push_up(rt);}
il ll query_range(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].sum;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll ans=0;if(L<=mid)ans+=query_range(L,R,rt << 1);
if(R>mid)ans+=query_range(L,R,rt << 1 | 1);return ans;}
il ll query_min(ll L,ll R,ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].minn;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll
ans=(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=min(ans,query_min(L,R,rt << 1));
if(R>mid)ans=min(ans,query_min(L,R,rt << 1 | 1));return ans;}
il ll query_max(ll L, ll R, ll rt)
{if(L<=tree[rt].l&&R>=tree[rt].r){return
tree[rt].maxn;}push_down(rt,tree[rt].r-tree[rt].l+1); ll
mid=(tree[rt].r+tree[rt].l)>>1;ll
ans=-(0x3f3f3f3f3f3f3f3fll);if(L<=mid)ans=max(ans,query_max(L,R,rt << 1));
if(R>mid)ans=max(ans,query_max(L,R,rt << 1 | 1));return ans;}
*/
const int N = 2e6 + 100;
struct Edge {
  int nex, to;
} edge[N << 1];
int head[N], tot;
void add_edge(int u, int v) {
  edge[++tot].nex = head[u];
  edge[tot].to = v;
  head[u] = tot;
}
int fac[N], inv[N];
void init() {
  fac[0] = 1;
  rep(i, 1, N - 10) fac[i] = fac[i - 1] * i % MOD;
  inv[N - 10] = pow_mod(fac[N - 10], MOD - 2, MOD);
  per(i, N - 11, 0) inv[i] = inv[i + 1] * (i + 1) % MOD;
}
int C(int n, int m) { return fac[n] * inv[n - m] % MOD * inv[m] % MOD; }
char s[N];
signed main() {
  ios;
  init();
  int k;
  cin >> k >> s + 1;
  int n = strlen(s + 1);
  int ans = 0;
  rep(i, 0, k) {
    ans += C(n + i - 1, n - 1) * pow_mod(25, i, MOD) % MOD *
           pow_mod(26, k - i, MOD) % MOD;
    ans %= MOD;
  }
  cout << ans << '\n';
  return 0;
}