#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,a,b) for(int i=a;i<b;i++)
using ll = long long;
using ull = unsigned long long;
using namespace std;

int px,py;
int qx,qy;
double ans = 0;

void solve()
{
    cin >> px >> py >> qx >> qy;
    while(px != qx) {
        if(abs(px - qx) == 1) {
            ans += 0.5;
            break;
        }
        else ans++;

        if(px < qx) {
            qx--;
            if(px == qx) break;
            px++;
            if(px == qx) break;
        }
        else if(qx < px) {
            px--;
            if(px == qx) break;
            qx++;
            if(px == qx) break;
        }
    }

    while(py != qy) {
        if(abs(py - qy) == 1) {
            ans += 0.5;
            break;
        }
        else ans++;

        if(py < qy) {
            qy--;
            if(py == qy) break;
            py++;
            if(py == qy) break;
        }
        else if(qy < py) {
            py--;
            if(py == qy) break;
            qy++;
            if(py == qy) break;
        }
    }
    cout << ans << endl;
}

int main(){cin.tie(0);ios_base::sync_with_stdio(false);solve();return 0;}