参考程序1：

#include<iostream>
using namespace std;

int first,second;
int m,n;
int sum = 0;

int fn(int n) {
	if(n==1) {
		return first;
	} else if (n==2) {
		return second;
	} else {
		return fn(n-1)+fn(n-2);
	}
}
int main() {
	cin>>first>>second;
	cin>>m>>n;
	sum = first+second;
	for(int i = 3; i<=n; i++) {
		sum+=fn(i);
		if(fn(i)>=m) {
			break;
		}
	}
	cout<<sum;
}

参考程序2：

#include<iostream>
using namespace std;
int main() {
	int a, b, m, n, ans, c;
	cin>>a>>b>>m>>n;
	ans = a+b;
	for(int i=3; i<=n; i++) {
		c = a+b;
		ans += c;
		a = b;
		b = c;
		if(c>=m) break;
	}
	cout<<ans;
}

参考程序3：

#include<iostream>
using namespace std;
int main() {
	int a, b, m, n, num, num1;
	cin>>a>>b>>m>>n;
	num = a+b;
	num1 = num+b;
	int z = a+b+num+num1;
	for(int i=5; i<=n; i++) {
		b = num;
		num = num1;
		num1 = b+num;
		z += num1;
		if(num1>=m) break;
	}
	cout<<z;
}