#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a,x,s;
	cin>>n>>a>>x;
	s=n-a*x;
	cout<<s;
}
/**************************************************************
	Problem: 1599
	User: zengyixuan
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/