#include <algorithm>
#include <iostream>
#include <fstream>
#include <set>
#include <string>

std::set<int> read_input_file() {
  std::ifstream file("input");
  std::set<int> data;
  std::string line;

  while(std::getline(file, line)) 
    data.insert(std::stoi(line));

  return data;
}

int main(){
  auto data = read_input_file();
  int iterations = 0;

  for(auto &i: data) {
    int rest = 2020 - i;
    for(auto &j: data) {
      int second_rest = rest - j;
      if (data.count(second_rest)) {
        std::cout << i * j * second_rest << std::endl;
        return 0;
      }
    }
  }

  return 1;
}