洛谷 B3923 [GESP202312 二级] 小杨做题

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
int main() {
	LL a, b, m, sum = 0, n, c = 0;
	cin >> a >> b >> m >> n;

	if (a == 0 && b == 0) {
		cout << 0 << endl;
		return 0;
	}
	sum = a + b;
	for (LL i = 3; i <= n; i ++) {
		if (c >= m) {
			break;
		}
		c = b + a;
		a = b;
		b = c;
		sum += c;
	}

	cout << sum << endl;
	return 0;
}