#include<bits/stdc++.h> using namespace std; int main(){ int x1,y1,x2,y2,x,y; cin>>x1>>y1; cin>>x2>>y2; x=abs(x1-x2); y=abs(y1-y2); if(x>y){ cout<<x<<endl; } else{ cout<<y<<endl; } return 0; }