#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <cmath>
#include <climits>
#include <iomanip>
#include <set>
#include <map>
using namespace std;
typedef long long ll;
int main(){
    ll a,b,c,d;
    cin >> a >> b >> c >> d;
    if(a > c)swap(a,c),swap(b,d);
    cout << b - a + 1 + d - c + 1 + max((ll)0,b - c + 1) << endl;
}