#include<cstdio>

#include<cstring>

#include<cmath>

#include<stack>

#include<vector>

#include<string>

#include<iostream>

#include<algorithm>

using namespace std;

int sx,sy;

int ex,ey;

int main()

{

    scanf("%d%d",&sx,&sy);

    scanf("%d%d",&ex,&ey);

    int ans;

    int lenx=abs(ex-sx);

    int leny=abs(ey-sy);

    ans=min(lenx,leny)+lenx-min(lenx,leny)+leny-min(lenx,leny);

    printf("%d\n",ans);

    return ;

}