80分 #2，#8 WA 救救我！！！

#include<iostream>
using namespace std;
int m,n;
int main(){
	int fib[366];
	cin>>fib[1]>>fib[2]>>m>>n;
	long long sum=fib[1]+fib[2];
	for(int i=3;i<=n+3;i++){
		fib[i]=fib[i-1]+fib[i-2];
		sum+=fib[i];
		if(fib[i]>=m){
			break;
		}	
	}
	cout<<sum;
	return 0;
}