#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int x,y,a,b,m,n; cin>>x>>y>>a>>b; if (abs(x-a)>abs(y-b)){ cout<<abs(x-a)<<endl; } else { cout<<abs(y-b)<<endl; } return 0; }