#include <iostream>
#include <cstring>
using namespace std;
int list[3] = {1,1,1};
string s;
int num = 0;
bool flag = true;
int main()
{
	cin >> s;
	for (int i = 0; i < s.length(); i++)
	{
		if (s[i] >= '0' && s[i] <= '9')list[i] = int(s[i]) - 47;
		else
		{
			flag = false;
			break;
		}
	}
	if (flag == false) 
	{
		cout << "error" << endl;
		return 0;
	}
	num = list[0] * 100 + list[1] * 10 + list[2];
	cout << num * 2 << endl;
	return 0;
}