#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    ll a, b, t;
    cin >> a >> b >> t;

    ll ans = 12345678912345;

    if(b >= 1000){
        int i = 0;
        while(true){
            ll tmp = t - b * i;
            if(tmp <= 0){
                ans = min(ans, b * i);
                break;
            }
            ll cnt = (tmp - 1) / a + 1;
            ans = min(ans, b * i + a * cnt);
            i++;
        }
    }else{
        ll ans2 = t / (a * b) * (a * b);
        t %= (a * b);
        int i = 0;
        while(true){
            ll tmp = t - b * i;
            if(tmp <= 0){
                ans = min(ans, b * i + ans2);
                break;
            }
            ll cnt = (tmp - 1) / a + 1;
            ans = min(ans, ans2 + b * i + a * cnt);
            i++;
        }
    }
    

    cout << ans << endl;
    return 0;
}