#include <bits/stdc++.h>
using namespace std;
long long a,b,t,n,i,j,minn=LLONG_MAX;
int main(){
    cin>>a>>b>>t;
    n=min(a,(t+b-1)/b);
    for(i=0;i<=n;++i){
        j=(t-b*i+a-1)/a;
        minn=min(minn,a*j+b*i);
    }
    cout<<minn;
    return 0;
}