#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
ll INF = (1LL << 60) - 1;
int MOD = 1e9+7;

ll gcd (ll a,ll b){
    return b ? gcd(b,a%b) : a;
}
main(){
    ll A,B,T;
    cin >> A >> B >> T;
    
    ll ans = INF;
    int i;
    for(i = 0;i * i <= T && i * B <= T;i++){

        ans = min(ans, (T - B * i + A - 1) / A * A + B * i);
    }
    if(B * i >= T)ans = min(ans, B * i);
    cout << ans << endl;

}