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

int main() {
    int h1, h2, h3, h4;
    cin >> h1 >> h2 >> h3 >> h4;
    
    int L = h1;
    int D = h2;  
    if(abs(h3 - L) < abs(D - L) || 
       (abs(h3 - L) == abs(D - L) && h3 < D)) {
        D = h3;
    }
    if(abs(h4 - L) < abs(D - L) || 
       (abs(h4 - L) == abs(D - L) && h4 < D)) {
        D = h4;
    }
    
    cout << D << endl;
    return 0;
}