Problem p02696 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <climits>
#include <cmath>
#include <cstring>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <vector>
using namespace std;
#define etm                                                                    \
  cerr << "Time elapsed :" << clock() * 1000.0 / CLOCKS_PER_SEC << " ms" << '\n'
#define fastio                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define ll long long int
#define ull unsigned long long int
#define doub long double
#define mp make_pair
#define pb push_back
#define pii pair<int, int>
#define pdd pair<double, double>
#define pll pair<long long int, long long int>
#define vpl vector<pll>
#define vll vector<ll>
#define vb vector<bool>
#define vvbb vector<vb>
#define vi vector<int>
#define mi map<int, int>
#define mull map<ull, ull>
#define stp setprecision(20)
#define N 100005
#define rep(i, a, b, c) for (int i = (a); i <= (b); i += (c))
#define repb(i, a, b, c) for (int i = (a); i >= (b); i -= (c))
#define MOD 1000000007
#define ld long double
#define inf 1e18
#define mp make_pair
#define vpll vector<pair<ll, ll>>
#define vvpll vector<vector<pair<ll, ll>>>
#define vvll vector<vector<ll>>
#define vvii vector<vector<int>>
#define all(x) x.begin(), x.end()
#define fi first
#define se second
#define test                                                                   \
  ll T;                                                                        \
  cin >> T;                                                                    \
  while (T--)
#define isvowel(a) (a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u')
#define show(w, size)                                                          \
  for (ll i = 0; i < size; i++)                                                \
    cout << w[i] << " ";
#define print(a) cout << a << "\n";
#define pqll priority_queue<ll>
#define mset(dp, no) memset(dp, no, sizeof(dp))
#define umll unordered_map<ll, ll>
#define mll map<ll, ll>
#define input(a, n)                                                            \
  ll I;                                                                        \
  rep(I, 0, n - 1, 1) cin >> a[I];
#define countbit __builtin_popcount // Number of set bits .
#define fbo(k) find_by_order // K-th element in a set (counting from zero) .
#define ook(k) order_of_key  //  Number of items strictly smaller than k .
#define lb lower_bound
#define up upper_bound
#define in insert
// #define db(x) cout <<#x<<": "<<x<<'\n';
#define ordered_set                                                            \
  tree<int, null_type, less<int>, rb_tree_tag,                                 \
       tree_order_statistics_node_update>
using namespace std;
#define db(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << '\n';
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
ll gcd(ll a, ll b) {
  if (a < b)
    return gcd(b, a);
  else if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
ll isPrime(ll n) {
  ll p = (ll)sqrt(n);
  rep(i, 2, p, 1) if (n % i == 0) return 0;
  return 1;
} // reuturn 1 if prime
ll pow(ll b, ll e) {
  if (e == 0)
    return 1;
  else if (e % 2 == 0) {
    ll a = pow(b, e / 2);
    return a * a;
  } else {
    ll a = pow(b, e / 2);
    return b * a * a;
  }
}
ll powm(ll x, ll y, ll m = MOD) {
  x = x % m;
  ll res = 1;
  while (y) {
    if (y & 1)
      res = res * x;
    res %= m;
    y = y >> 1;
    x = x * x;
    x %= m;
  }
  return res;
}
ll ceil(long double a) {
  ll b = a;
  if (a == b) {
    return b;
  } else {
    return b + 1;
  }
}
ll floor(long double a) {
  ll b = a;
  return b;
}
ll lcm(ll a, ll b) { return (a * b) / gcd(a, b); }
ll modInverse(ll a, ll m) { return powm(a, m - 2, m); }
bool issq(ll n) {
  ll p = sqrt(n);
  return p * p == n;
}
vll prime; // if i==prime[i] then prime otherwise smallest prime factor of that
           // number
void sieve(ll n) {
  prime.resize(n + 1, 1);
  prime[0] = 0, prime[1] = 0;
  for (ll i = 2; i * i <= n; i++)
    if (prime[i])
      for (ll j = i * i; j <= n; j += i)
        prime[j] = 0;
}
ll extended_GCD(ll a, ll b, ll &x, ll &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  ll x1, y1;
  ll gcd = extended_GCD(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return gcd;
}
ll mulInv(ll a, ll mod = 26) {
  ll x, y;
  extended_GCD(a, mod, x, y);
  if (x < 0)
    x += mod;
  return x;
}
ll find(ll num[], ll rem[], ll k, ll prod) {
  // Compute product of all numbers
  ll result = 0;
  // Apply above formula
  for (ll i = 0; i < k; i++) {
    ll pp = prod / num[i];
    result += rem[i] * mulInv(pp, num[i]) * pp;
  }
  return result % prod;
}
ll nCr(ll n, ll k) {
  ll res = 1;

  // Since C(n, k) = C(n, n-k)
  if (k > n - k)
    k = n - k;

  // Calculate value of
  // [n * (n-1) *---* (n-k+1)] / [k * (k-1) *----* 1]
  for (ll i = 0; i < k; ++i) {
    res *= (n - i);
    res /= (i + 1);
  }

  return res;
}
class DSU {
public:
  vll parent, size;

public:
  DSU(ll n) {

    parent.resize(n + 1);
    size.resize(n + 1);
    for (ll i = 1; i <= n; i++) {
      parent[i] = i;
      size[i] = 1;
    }
  }

public:
  ll find_set(ll x) {
    if (parent[x] == x) {
      return x;
    }
    return parent[x] = find_set(parent[x]);
  }

public:
  void union_set(ll x, ll y) {
    x = find_set(x);
    y = find_set(y);
    if (x != y) {
      parent[y] = x;
    }
  }
};
bool cmp(pair<ll, ll> &p1, pair<ll, ll> &p2) {
  if (p1.fi == p2.fi) {
    return p1.se > p2.se;
  }
  return p1.fi > p2.fi;
}
bool isPalindrome(string s) {
  ll i, j;
  for (i = 0, j = s.length() - 1; i <= j; i++, j--) {
    if (s[i] != s[j]) {
      return 0;
    }
  }
  return 1;
}
ll ToInt(char ch) { return ch - '0'; }
char ToChar(ll a) { return a + '0'; }
bool isSubSeq(string str1, string str2, ll m, ll n) {
  // Base Cases
  if (m == 0)
    return true;
  if (n == 0)
    return false;
  // If last characters of two strings are matching
  if (str1[m - 1] == str2[n - 1])
    return isSubSeq(str1, str2, m - 1, n - 1);
  // If last characters are not matching
  return isSubSeq(str1, str2, m, n - 1);
}
void printVectorPair(vpll v) {
  for (ll i = 0; i < v.size(); i++) {
    cout << v[i].fi << " " << v[i].se << "\n";
  }
}
void modBigNumber(string num, ll m) {
  // Store the modulus of big number
  vector<int> vec;
  ll mod = 0;
  // Do step by step division
  for (int i = 0; i < num.size(); i++) {
    int digit = num[i] - '0';
    mod = mod * 10 + digit;
    int quo = mod / m;
    if ((vec.size() != 0) || (quo != 0)) // to remove initiale zeros
      vec.push_back(quo);
    mod = mod % m;
  }
  // cout << "\nRemainder : " << mod << "\n";
  // cout << "Quotient : ";rep(i,0,vec.size()-1,1)cout<<vec[i];cout<<"\n";
  return;
}
struct SegmentTree {
  ll n;
  vll v;
  SegmentTree(ll size) {
    n = 4 * size + 1;
    v.resize(n, 0);
  }
  void build(ll ar[], ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return;
    if (ipos == fpos)
      v[pos] = ar[ipos];
    else {
      ll mid = (ipos + fpos) / 2;
      build(ar, ipos, mid, pos * 2);
      build(ar, mid + 1, fpos, pos * 2 + 1);
      v[pos] = v[pos * 2] + v[pos * 2 + 1];
    }
  }
  void update(ll index, ll val, ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return;
    if (ipos == fpos)
      v[pos] += val;
    else {
      v[pos] += val;
      ll mid = (ipos + fpos) / 2;
      if (mid >= index)
        update(index, val, ipos, mid, pos * 2);
      else
        update(index, val, mid + 1, fpos, pos * 2 + 1);
    }
  }
  ll get_sum(ll l, ll r, ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return 0;
    if (l > r)
      return 0;
    ll mid = (ipos + fpos) / 2;
    if ((l == ipos) && (r == fpos))
      return v[pos];
    else
      return get_sum(l, min(mid, r), ipos, mid, pos * 2) +
             get_sum(max(mid + 1, l), r, mid + 1, fpos, pos * 2 + 1);
  }
};
struct BIT {
  vector<ll> bitree;
  ll n;
  BIT(ll n) {
    this->n = n;
    bitree.resize(n + 1, 0);
  }
  void update(ll idx, ll val) {
    idx++;
    while (idx <= n) {
      bitree[idx] += val;
      idx += idx & (-idx);
    }
  }
  ll Sum(ll idx) {
    ll sum = 0;
    idx++;
    while (idx > 0) {
      sum += bitree[idx];
      idx -= idx & (-idx);
    }
    return sum;
  }
};
ll sumofdigits(ll a) {
  ll val = 0;
  while (a > 0) {
    val += a % 10;
    a /= 10;
  }
  return val;
}

/*
ideas
*/

int main() {
  fastio;
  ll n, a, b, ans = LLONG_MIN;
  cin >> a >> b >> n;
  rep(i, 1, min(n, (ll)1e12), 1) {
    ans = max(ans, ((a * i) / b) - (a * (i / b)));
  }
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <climits>
#include <cmath>
#include <cstring>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <vector>
using namespace std;
#define etm                                                                    \
  cerr << "Time elapsed :" << clock() * 1000.0 / CLOCKS_PER_SEC << " ms" << '\n'
#define fastio                                                                 \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);
#define ll long long int
#define ull unsigned long long int
#define doub long double
#define mp make_pair
#define pb push_back
#define pii pair<int, int>
#define pdd pair<double, double>
#define pll pair<long long int, long long int>
#define vpl vector<pll>
#define vll vector<ll>
#define vb vector<bool>
#define vvbb vector<vb>
#define vi vector<int>
#define mi map<int, int>
#define mull map<ull, ull>
#define stp setprecision(20)
#define N 100005
#define rep(i, a, b, c) for (int i = (a); i <= (b); i += (c))
#define repb(i, a, b, c) for (int i = (a); i >= (b); i -= (c))
#define MOD 1000000007
#define ld long double
#define inf 1e18
#define mp make_pair
#define vpll vector<pair<ll, ll>>
#define vvpll vector<vector<pair<ll, ll>>>
#define vvll vector<vector<ll>>
#define vvii vector<vector<int>>
#define all(x) x.begin(), x.end()
#define fi first
#define se second
#define test                                                                   \
  ll T;                                                                        \
  cin >> T;                                                                    \
  while (T--)
#define isvowel(a) (a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u')
#define show(w, size)                                                          \
  for (ll i = 0; i < size; i++)                                                \
    cout << w[i] << " ";
#define print(a) cout << a << "\n";
#define pqll priority_queue<ll>
#define mset(dp, no) memset(dp, no, sizeof(dp))
#define umll unordered_map<ll, ll>
#define mll map<ll, ll>
#define input(a, n)                                                            \
  ll I;                                                                        \
  rep(I, 0, n - 1, 1) cin >> a[I];
#define countbit __builtin_popcount // Number of set bits .
#define fbo(k) find_by_order // K-th element in a set (counting from zero) .
#define ook(k) order_of_key  //  Number of items strictly smaller than k .
#define lb lower_bound
#define up upper_bound
#define in insert
// #define db(x) cout <<#x<<": "<<x<<'\n';
#define ordered_set                                                            \
  tree<int, null_type, less<int>, rb_tree_tag,                                 \
       tree_order_statistics_node_update>
using namespace std;
#define db(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1> void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << '\n';
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
ll gcd(ll a, ll b) {
  if (a < b)
    return gcd(b, a);
  else if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
ll isPrime(ll n) {
  ll p = (ll)sqrt(n);
  rep(i, 2, p, 1) if (n % i == 0) return 0;
  return 1;
} // reuturn 1 if prime
ll pow(ll b, ll e) {
  if (e == 0)
    return 1;
  else if (e % 2 == 0) {
    ll a = pow(b, e / 2);
    return a * a;
  } else {
    ll a = pow(b, e / 2);
    return b * a * a;
  }
}
ll powm(ll x, ll y, ll m = MOD) {
  x = x % m;
  ll res = 1;
  while (y) {
    if (y & 1)
      res = res * x;
    res %= m;
    y = y >> 1;
    x = x * x;
    x %= m;
  }
  return res;
}
ll ceil(long double a) {
  ll b = a;
  if (a == b) {
    return b;
  } else {
    return b + 1;
  }
}
ll floor(long double a) {
  ll b = a;
  return b;
}
ll lcm(ll a, ll b) { return (a * b) / gcd(a, b); }
ll modInverse(ll a, ll m) { return powm(a, m - 2, m); }
bool issq(ll n) {
  ll p = sqrt(n);
  return p * p == n;
}
vll prime; // if i==prime[i] then prime otherwise smallest prime factor of that
           // number
void sieve(ll n) {
  prime.resize(n + 1, 1);
  prime[0] = 0, prime[1] = 0;
  for (ll i = 2; i * i <= n; i++)
    if (prime[i])
      for (ll j = i * i; j <= n; j += i)
        prime[j] = 0;
}
ll extended_GCD(ll a, ll b, ll &x, ll &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  ll x1, y1;
  ll gcd = extended_GCD(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return gcd;
}
ll mulInv(ll a, ll mod = 26) {
  ll x, y;
  extended_GCD(a, mod, x, y);
  if (x < 0)
    x += mod;
  return x;
}
ll find(ll num[], ll rem[], ll k, ll prod) {
  // Compute product of all numbers
  ll result = 0;
  // Apply above formula
  for (ll i = 0; i < k; i++) {
    ll pp = prod / num[i];
    result += rem[i] * mulInv(pp, num[i]) * pp;
  }
  return result % prod;
}
ll nCr(ll n, ll k) {
  ll res = 1;

  // Since C(n, k) = C(n, n-k)
  if (k > n - k)
    k = n - k;

  // Calculate value of
  // [n * (n-1) *---* (n-k+1)] / [k * (k-1) *----* 1]
  for (ll i = 0; i < k; ++i) {
    res *= (n - i);
    res /= (i + 1);
  }

  return res;
}
class DSU {
public:
  vll parent, size;

public:
  DSU(ll n) {

    parent.resize(n + 1);
    size.resize(n + 1);
    for (ll i = 1; i <= n; i++) {
      parent[i] = i;
      size[i] = 1;
    }
  }

public:
  ll find_set(ll x) {
    if (parent[x] == x) {
      return x;
    }
    return parent[x] = find_set(parent[x]);
  }

public:
  void union_set(ll x, ll y) {
    x = find_set(x);
    y = find_set(y);
    if (x != y) {
      parent[y] = x;
    }
  }
};
bool cmp(pair<ll, ll> &p1, pair<ll, ll> &p2) {
  if (p1.fi == p2.fi) {
    return p1.se > p2.se;
  }
  return p1.fi > p2.fi;
}
bool isPalindrome(string s) {
  ll i, j;
  for (i = 0, j = s.length() - 1; i <= j; i++, j--) {
    if (s[i] != s[j]) {
      return 0;
    }
  }
  return 1;
}
ll ToInt(char ch) { return ch - '0'; }
char ToChar(ll a) { return a + '0'; }
bool isSubSeq(string str1, string str2, ll m, ll n) {
  // Base Cases
  if (m == 0)
    return true;
  if (n == 0)
    return false;
  // If last characters of two strings are matching
  if (str1[m - 1] == str2[n - 1])
    return isSubSeq(str1, str2, m - 1, n - 1);
  // If last characters are not matching
  return isSubSeq(str1, str2, m, n - 1);
}
void printVectorPair(vpll v) {
  for (ll i = 0; i < v.size(); i++) {
    cout << v[i].fi << " " << v[i].se << "\n";
  }
}
void modBigNumber(string num, ll m) {
  // Store the modulus of big number
  vector<int> vec;
  ll mod = 0;
  // Do step by step division
  for (int i = 0; i < num.size(); i++) {
    int digit = num[i] - '0';
    mod = mod * 10 + digit;
    int quo = mod / m;
    if ((vec.size() != 0) || (quo != 0)) // to remove initiale zeros
      vec.push_back(quo);
    mod = mod % m;
  }
  // cout << "\nRemainder : " << mod << "\n";
  // cout << "Quotient : ";rep(i,0,vec.size()-1,1)cout<<vec[i];cout<<"\n";
  return;
}
struct SegmentTree {
  ll n;
  vll v;
  SegmentTree(ll size) {
    n = 4 * size + 1;
    v.resize(n, 0);
  }
  void build(ll ar[], ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return;
    if (ipos == fpos)
      v[pos] = ar[ipos];
    else {
      ll mid = (ipos + fpos) / 2;
      build(ar, ipos, mid, pos * 2);
      build(ar, mid + 1, fpos, pos * 2 + 1);
      v[pos] = v[pos * 2] + v[pos * 2 + 1];
    }
  }
  void update(ll index, ll val, ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return;
    if (ipos == fpos)
      v[pos] += val;
    else {
      v[pos] += val;
      ll mid = (ipos + fpos) / 2;
      if (mid >= index)
        update(index, val, ipos, mid, pos * 2);
      else
        update(index, val, mid + 1, fpos, pos * 2 + 1);
    }
  }
  ll get_sum(ll l, ll r, ll ipos, ll fpos, ll pos = 1) {
    if (ipos > fpos)
      return 0;
    if (l > r)
      return 0;
    ll mid = (ipos + fpos) / 2;
    if ((l == ipos) && (r == fpos))
      return v[pos];
    else
      return get_sum(l, min(mid, r), ipos, mid, pos * 2) +
             get_sum(max(mid + 1, l), r, mid + 1, fpos, pos * 2 + 1);
  }
};
struct BIT {
  vector<ll> bitree;
  ll n;
  BIT(ll n) {
    this->n = n;
    bitree.resize(n + 1, 0);
  }
  void update(ll idx, ll val) {
    idx++;
    while (idx <= n) {
      bitree[idx] += val;
      idx += idx & (-idx);
    }
  }
  ll Sum(ll idx) {
    ll sum = 0;
    idx++;
    while (idx > 0) {
      sum += bitree[idx];
      idx -= idx & (-idx);
    }
    return sum;
  }
};
ll sumofdigits(ll a) {
  ll val = 0;
  while (a > 0) {
    val += a % 10;
    a /= 10;
  }
  return val;
}

/*
ideas
*/

int main() {
  fastio;
  ll n, a, b, ans = LLONG_MIN;
  cin >> a >> b >> n;
  if (n >= b) {
    cout << (a * (b - 1)) / b - a * ((b - 1) / b) << endl;
  } else {
    cout << (a * n) / b - a * (n / b) << endl;
  }
  return 0;
}