//dfs 但是有一些细节问题需要注意
#include <bits/stdc++.h>

using namespace std;
const int N = 2e2 + 10;
const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3f;
const unsigned long long P = 1e9 + 7;
const double eps = 1e-6;
string s;
int a[N],b[N],c[N];
int Max = 0;
//判断到当前位数下是否符合条件
bool check(int pos){
    memset(c,0,sizeof c);
    for(int i = 0;i<=pos;i++){
        for(int j = 0;j<=pos;j++){
            if(pos!=Max-1&&i+j>pos) break;
            c[i+j] += (b[i]*b[j])%10;
            c[i+j] %= 10;
        }
    }
    for(int i = 0;i<=(pos==Max-1?Max*2-2:pos);i++){
        if(c[i]!=a[i])  return false;
    }
    return true;
}
//dfs找
void dfs(int pos){
    if(pos==Max){
        if(!check(pos-1))    return;
        for(int j = 0;j<pos;j++) cout<<b[j];
        exit(0);
    }
    for(int i = 0;i<=9;i++){
        b[pos] = i;
        if(check(pos)){
            dfs(pos+1);
        }
    }
}
int main() {
    cin>>s;
    int n = s.size();
    if(n%2==0) {
        cout<<"-1\n";
        return 0;
    }
    for(int i = 0;i<s.size();i++){
        a[i] = s[i]-'0';
    }
    Max = (n+1)/2;
    dfs(0);
    cout<<"-1\n";
    return 0;
}

//找到两两可以放入同一个集合的单词 跑一遍二分图
#include <bits/stdc++.h>

using namespace std;
const int N = 505;
char str[N][30];
int match[N];
bool vis[N];
vector<int> g[N];

bool check(char s[], char str[], int n) {
    int num = 0;
    for (int i = 0; i < n; i++)
        if (s[i] != str[i]) num++;
    return num == 2;
}

bool dfs(int u) {
    for (int i = 0, v; i < g[u].size(); i++) {
        if (!vis[v = g[u][i]]) {
            vis[v] = true;
            if (!match[v] || dfs(match[v])) {
                match[v] = u;
                return true;
            }
        }
    }
    return false;
}

int Get(int n) {
    memset(match, 0, sizeof match);
    int num = 0;
    for (int i = 1; i <= n; i++) {
        memset(vis, 0, sizeof vis);
        if (dfs(i)) num++;
    }
    return num / 2;
}

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        scanf("%s", str[i]);
    }
    int len = strlen(str[1]);
    for (int i = 1; i <= n; i++)
        for (int j = 1; j < i; j++)
            if (check(str[i], str[j], len)) {
                g[i].push_back(j);
                g[j].push_back(i);
            }
    int res = n - Get(n);
    printf("%d\n", res);
    return 0;
}

//签到题 暴力跑一遍
#include <bits/stdc++.h>

using namespace std;
set<string> se;
string s, str;

int main() {
    ios::sync_with_stdio(false);
    cin >> s >> str;
    for (int i = 0; i < str.size(); i++) {
        string s2 = str;
        auto it = s2.begin() + i;
        s2.erase(it);
        se.insert(s2);
    }
    for (auto c : s) {
        for (int i = 0; i < str.size(); i++) {
            char cc = str[i];
            if (c == cc) continue;
            str[i] = c;
            se.insert(str);
            str[i] = cc;
            se.insert(str.substr(0, i) + c +
                      str.substr(i, (int)str.size() - i));
        }
        se.insert(str + c);
    }
    for (auto ss : se) {
        cout << ss << '\n';
    }
    return 0;
}