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