#include <cmath>
#include <map>
#include <string>
#include <vector>
#include <set>
#include <algorithm>
#include <iostream>
using namespace std;
#define repi(_I, _B, _E) for(int _I = (_B); (_I) < (_E); ++ (_I))
#define rep(_I, _N) for(int _I = 0; (_I) < (_N); ++ (_I))
#define all(_X) (_X).begin(), (_X).end()

using ll = long long;
int a, b, t;

int main() {
	cin >> a >> b >> t;
	
	ll mi = 2000000000;
	for ( ll y = 0; y < a && y * b < t + b; ++y ) {
		ll x = (t - b * y + a - 1)/a;
		mi = min(mi, a * x + b * y);
	}
	cout << mi << endl;
	return 0;
}