#include <bits/stdc++.h>
using namespace std;
int main(){

	int i,n,s,b,c;
	cin>>i>>n>>s;
	b=n*s;
	c=i-b;
	cout<<c;
	
	return 0;
}
/**************************************************************
	Problem: 1599
	User: huangyaojie3
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/