#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int x1,y1,x2,y2; cin>>x1>>y1>>x2>>y2; if(abs(x1-x2)>abs(y1-y2)){ cout<<abs(x1-x2); } else{ cout<<abs(y1-y2); } return 0; }