#include <iostream>      // cout, endl, cin
#include <string>        // string, to_string, stoi
#include <vector>        // vector
#include <algorithm>     // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility>       // pair, make_pair
#include <tuple>         // tuple, make_tuple
#include <cstdint>       // int64_t, int*_t
#include <cstdio>        // printf
#include <map>           // map
#include <cmath>         // sqrt
#include <queue>         // queue, priority_queue
#include <set>           // set
#include <stack>         // stack
#include <deque>         // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset>        // bitset
#include <bits/stdc++.h> // isupper, islower, isdigit, toupper, tolower
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, n) for (int i = (a); i < (n); i++)
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> Pl;
typedef pair<int, int> P;
typedef tuple<ll, ll, string> Tlls;

int main()
{
  ll A, B, N;
  cin >> A >> B >> N;
  ll ans = 0;
  ll x = min(B - 1, N);
  ll tmp = floor(A * x / B) - A * floor(x / B);

  ans = max(ans, tmp);

  cout << ans << endl;
  return 0;
}
