#include <fstream>
#include <iostream>
#include <vector>
#include <bitset>
#include <string.h>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <deque>
#include <stdio.h>

using namespace std;

const char infile[] = "spell.in";
const char outfile[] = "spell.out";

ifstream fin(infile);
ofstream fout(outfile);

const int MAXN = 100005;
const int oo = 0x3f3f3f3f;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

int v[5];

int main() {
    scanf("%d %d %d %d", &v[1], &v[2], &v[3], &v[4]);
    sort(v + 1, v + 4 + 1);
    printf("%d\n", v[1] * v[2] + v[3] * v[4]);
    fin.close();
    fout.close();
    return 0;
}