#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; int x,y; cin>>a>>b>>c>>d; x=a-c; y=b-d; if(x<0) x=-x; if(y<0) y=-y; if(x>y) cout<<x<<endl; else cout<<y<<endl; return 0; }