要注意用ceil()去向上取整

#include <bits/stdc++.h>
using namespace std;
int main(){
	int n,x,y;
    cin>>n>>x>>y;
    if(x==0) {
        cout<<n;
        return 0;
    }
    if(n-ceil(y/1.0/x) < 0){
        cout<<0;
        return 0;
    }
    cout<<n-ceil(y/1.0/x);
	return 0;
}