#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

string ans = "";
string s;
int len;

string mult(string t)
{
	string res(2 * SZ(t) - 1, '0');
	FOR (i, 0, SZ(t))
	{
		FOR (j, 0, SZ(t))
		{
			int x = (t[i] - '0') * (t[j] - '0') % 10;
			res[i + j] = (((res[i + j] - '0') + x) % 10) + '0';
		}
	}
	//cerr << t << ' ' << res << '\n';
	return res;
}

void upd(string t)
{
	reverse(ALL(t));
	if (ans.empty() || SZ(ans) > SZ(t))
		ans = t;
	if (ans > t)
		ans = t;
}

void f(string t)
{
	if (SZ(t) == len)
	{
		if (s == mult(t))
			upd(t);
		return;
	}
	FOR (d, 0, 10)
	{
		int res = 0;
		int pos = SZ(t);
		t += (d + '0');
		FOR (i, 0, pos + 1)
		{
			res += (t[i] - '0') * (t[pos - i] - '0');
			res %= 10;
		}
		//cerr << d << ' ' << t << ' ' << res << '\n';
		if (res == s[pos] - '0')
			f(t);
		t.pop_back();
	}
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> s;
	if (SZ(s) % 2 == 0)
	{
		cout << -1 << '\n';
		return 0;
	}
	len = SZ(s) / 2 + 1;
	reverse(ALL(s));
	f("");
	if (ans.empty())
		cout << -1 << '\n';
	else
		cout << ans << '\n';
	
	return 0;
}