#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 a,b,c,d,e,f; cin>>a>>b>>c>>d; e=a-c; f=b-d; if(abs(e)>abs(f)) cout<<abs(e); else cout<<abs(f); return 0; }