#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
    int A[4];
    for( int i = 0; i < 4; ++i )
        cin >> A[i];
    sort( A, A + 4 );
    cout << ((A[0] * A[1]) + (A[2] * A[3]));
    return 0;
}