#include<bits/stdc++.h>
using namespace std;
int main() {
	int n,a,x,s;
	scanf("%d %d %d",&n,&a,&x);
	s=n-a*x;
	printf("%d",s);
    return 0;
}

/**************************************************************
	Problem: 1599
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/