C++ :

#include<bits/stdc++.h>
using namespace std;
int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
long long a,b,n;
cin>>a>>b>>n;  //容积 初始量 数量
long long k=a/b;
if(k<=n)	cout<<b*k;
else		cout<<b*n;

return 0;
}