为什么只有80分

#include<bits/stdc++.h>
using namespace std;
int a, b, c, s, n, q;
int main() {
	cin >> a >> b;
	cin >> c;
	s = a - c;
	if (s < 0) {
		n++;
	} else {
		q = s;
	}
	for (int i = 2; i <= b; i++) {
		cin >> c;
		s = q - c;
		if (s < 0) {
			n++;
		} else {
			q = s;
		}
	}
	cout<<n;
	return 0;
}

错了第三个