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