#include <stdio.h>
#include <iostream>
#include <vector>
#include <map>
#include <queue>
#include <algorithm>
#include <set>
#include <math.h>
#include <string>
#include <stdlib.h>
#include <string.h>
#include <iomanip>
using namespace std;

typedef pair<int, int> pii;
#define ll long long
#define INF 1e9



int main()
{
  //  freopen("C:\\in.txt", "r", stdin);
    int a,b,c,d;
    int x;
    int n=4;
    vector<int> v;
    while(n--){
        scanf("%d", &x);
        v.push_back(x);
    }
    sort(v.rbegin(), v.rend());
    cout << v[0] * v[1] + v[2]*v[3] << endl;

    return 0;
}