#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <cstdio>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(n);i++)
const ll INF = 1e12;

int main(void){
	ll a, b, t; cin >> a >> b >> t;
	ll ans = INF;
	for (int i = 0; i <= 1e9; ++i){//bの数
		if(b * i <= t){
			int nokori = t - b * i;
			int j;
			if(nokori % a == 0){
				j = nokori / a;
			}else{
				j = nokori / a + 1;
			}
			ans = min(ans, (ll)(b * i + a * j));
		}else{
			//bの数のみで超えるとき
			ans = min(ans, (ll)(b * i));
			break;
		}
	}
	printf("%d\n", ans);
	return 0;
}