#include<iostream> // cin\cout\endl using namespace std; int main(){ int x,y,x1,y1,x2,y2; 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; }