#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <numeric>
#include <regex>
#include <tuple>
#include <iomanip>
#include <cmath>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
#define MOD 1000000007 // 10^9 + 7
#define INF 1000000000 // 10^9
#define LLINF 1LL<<60


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll A, B, T; cin >> A >> B >> T;
	ll ans = LLINF;

	for (ll i = 0; i <= A && i*B <= T + B; i++) {

		ll j;
		if (i*B >= T) j = 0;
		else {
			j = (T - i * B) / A;
			if ((T - i * B) % A != 0) j++;
		}

		ll K = A * j + B * i;
		ans = min(ans, K);
	}

	cout << ans << endl;

	return 0;
}