import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int t = in.nextInt();
        int b = in.nextInt();
        int f = in.nextInt();
        int c = in.nextInt();
        long totEdges = (long)t;
        totEdges *= t+1;
        totEdges /= 2;
        if ((long)t+b+f+c != totEdges)
            System.out.println(-1);
    }
}