#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(int i=0; i<(n); i++)

int A, B, T;
signed main()
{
    cin >> A >> B >> T;
    int maxb = (T + B - 1) / B;
    int minC = 1e9 + 100;
    REP(i,maxb+1) {
        int cost = i * B;
        int remain = T - cost;
        int numa = (remain + A - 1) / A;
        cost += numa * A;
        minC = min(minC, cost);
        if (minC == T) break;
    }
    cout << minC << endl;
    return 0;
}