#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < n; i++)
typedef long long int64;
const int64 INF = 1LL << 55;
int main()
{
  int64 A, B, T;
  cin >> A >> B >> T;
  int64 ret = INF;
  rep(i, 100000001) {
    int64 BN = i;
    int64 Need = T - B * i; // Needを上回るやつだから
    int64 AN = (Need + A - 1) / A;
    int64 Money = 1LL * AN * A + 1LL * BN * B;
    ret = min(ret, Money);
  }
  cout << ret << endl;
}