#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;

int64 A, B, T;
int64 ret = INF;
int64 Need;
int main()
{
  cin >> A >> B >> T;
  Need = T + B;
  rep(i, 10000000) {
    Need -= B;
    ret = min(ret, (Need + A - 1) / A * A + i * B);
  }
  cout << ret << endl;
}