#include <bits/stdc++.h> using namespace std; int main(){int h[4];for(int&i:h)cin>>i;int ans=h[1];for(int i=2;i<4;i++)if(abs(h[i]-h[0])<abs(ans-h[0])||(abs(h[i]-h[0])==abs(ans-h[0])&&h[i]<ans))ans=h[i];cout<<ans<<"\n";}