#include<iostream>
using namespace std;
int main()
{
	int n,m,p,c;
	while(1)
	{
		cin>>n>>m>>p>>c;
		if(n==0&&m==0&&p==0&&c==0)
			return 1;
		if(m>p)
			cout<<n-m+p<<endl;
		else
			cout<<n+c<<endl;
	}
	return 1;
}