#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000
#define int long long

signed main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int A, B, T;
	cin >> A >> B >> T;
	int Y = 0;
	int ans = ((T + A - 1) / A) * A;
	while (true) {
		int X = (T - B * Y + A - 1) / A;
		ans = min(ans, X * A + Y * B);
		if (Y > A || B * Y > T) break;
		Y++;
	}
	cout << ans << endl;


    return 0;
}