#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a,x,i;
	cin>>n>>a>>x;
	i=n-x*a;
	cout<<i;
} 
/**************************************************************
	Problem: 1599
	User: huxuanchen
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/