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