#include<bits/stdc++.h>
using namespace std;
int main(){
	int x,a,n;
	cin>>n>>x>>a;
	cout<<n-(a*x);
	return 0;
}
/**************************************************************
	Problem: 1599
	User: chenyaohuo
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/