#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,a,x,b;
    cin>>n>>a>>x;
    b=n-(a*x);
    printf("%d",b);
}
/**************************************************************
	Problem: 1599
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/