// Author: Olaf Surgut (surgutti)
// Created on 01-10-2024 12:56:17
#include <bits/stdc++.h>
using namespace std;

#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif

#define endl '\n'
#define st first
#define nd second
#define pb push_bask
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define ROF(i, b, a) for (int i = (b); i >= (a); i--)
#define REP(i, n) for (int i = 0; i < (n); i++)

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	vector<int> a(4);
	for (int& x : a)
		cin >> x;
	
	sort(a.begin(), a.end());

	int ans = 0;
	do {
		ans = max(ans, min(a[0], a[1]) * min(a[2], a[3]));
	} while (next_permutation(a.begin(), a.end()));

	cout << ans << '\n';

	return 0;
}