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;
}