C++ :

#include <bits/stdc++.h>
using namespace std;

int main(){
	int a,b,c,m,n;
	int s = 0;
	cin>>a>>b>>m>>n;
	s = a+b;
	for(int i=3;i<=n;i++){
		c = b+a;
		s += c;
		a = b;
		b = c;
		if(c >= m){
			break;
		}
	}
	cout<<s;
}