#include <cstdio>
#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <cstring>
#include <string>
#include <ctime>
#include <cassert>
#include <utility>

using namespace std;

int A[5];

int main() {
//	freopen("date.in", "r", stdin);
	
	for(int i = 0; i < 4; i++)
        scanf("%d", &A[i]);
    
    vector<int> perm(4);
    for(int i = 0; i < 4; i++)
        perm[i] = i;
    
    int ans = 0;
	do {
	    int a = A[perm[0]];
	    int b = A[perm[1]];
	    int c = A[perm[2]];
	    int d = A[perm[3]];
        ans = max(ans, a * b + c * d);
	} while(next_permutation(perm.begin(), perm.end()));
	
	printf("%d\n", ans);
	
	return 0;
}