/** gnu specific **/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/** contains everything I need in std **/
#include <bits/stdc++.h>

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(S) ((int)S.size())
#define FOR(i, st_, n) for(int i = st_; i < n; ++i)
#define RFOR(i, n, end_) for(int i = (n)-1; i >= end_; --i)
#define x first
#define y second
#define pb push_back
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ull, ull> pull;
using namespace __gnu_pbds;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace std;
#ifdef ONPC
mt19937 rnd(228);
#else
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif


bool check(string cur, string s)
{
    string res = "";
    FOR(i,0,sz(s))
        res+='0';
    FOR(i,0,sz(cur))
        FOR(j,0,sz(cur))
        {
            res[i+j] = to_string(((res[i+j]-'0')+ (cur[i]-'0')*(cur[j]-'0'))%10)[0];
        }
    if(res == s)
        return true;
    return false;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    string s;
    cin >> s;
    ll n = sz(s);
    if(n%2 == 0){
        cout << -1;
        return 0;
    }
    string resul = "";
    n = (n+1)/2;
    queue<string> que;
    que.push("");
    while(!que.empty())
    {
        string cur = que.front();
        que.pop();
        if(sz(cur) == n)
        {
            if(check(cur,s))
                if(resul == "")
                    resul = cur;
                else
                    resul = min(resul,cur);
        }
        FOR(j,0,10)
        {
            ll c = 0;
            string cr = cur + to_string(j);
            FOR(u,0,sz(cr))
            {
                c += ((cr[u]-'0')*(cr[sz(cr)-u-1]-'0'));
            }
            c%=10;
            if(to_string(c)[0] == s[sz(cr)-1]){
                que.push(cr);
            }
        }
    }
    if(resul == "")
        cout << -1 << endl;
    else
        cout << resul;
}