#include<bits/stdc++.h>
using namespace std;
#define ll long long
typedef pair<ll,ll> P;
#define M 1000000007
int main(){
  ll a,b,c,d,e;
  cin>>a>>b>>c>>d;
  e=(b-a+1)*(d-c+1);
  for(int i=0;i<=100;i++){
    if(i>=a&&i<=b&&i>=c&&i<=d) e--;
  }
  cout<<"e"<<endl;
}