#include <iostream>
#include <algorithm>
using namespace std;

int main() {
	int v[4],rez=-(1<<30);
	cin>>v[0]>>v[1]>>v[2]>>v[3];
	do {
		rez=max(rez,v[0]*v[1]+v[2]*v[3]);
	}while(next_permutation(v,v+4));
	cout<<rez;
}