#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 25,M = 7,C = 1e4+10;
typedef array<int,M> vec;
int z[N],val[N],n,m,k,pw[M+1],tmp[N];

vec p[C],q[C]; int pc,qc;

int main(){
    pw[0] = 1; for(int i=1;i<=M;i++)pw[i] = pw[i-1] * 10;

    string s; cin>>s; n = s.length();
    for(int i=0;i<n;i++)z[i] = s[n-1-i] - '0';
    if(n%2==0){cout<<"-1\n"; return 0;}
    if(n==1){
        if(z[0] == 1)cout<<"1\n";
        else if(z[0] == 4)cout<<"2\n";
        else if(z[0] == 9)cout<<"3\n";
        else if(z[0] == 6)cout<<"4\n";
        else if(z[0] == 5)cout<<"5\n";
        else cout<<"-1\n";
        return 0;
    }
    m = (n+1)/2,k = m/2; //[0,k) 和 [k,m) 两部分

    for(int i=0;i<pw[k];i++){
        vec now = {};
        int num = i; for(int x=0;x<k;x++)now[x] = num%10,num /= 10;
        memset(tmp,0,sizeof tmp);
        for(int x=0;x<k;x++)for(int y=0;x+y<k;y++)tmp[x+y] += now[x] * now[y];
        int flag = 1; for(int x=0;x<k;x++)flag &= (tmp[x]%10) == z[x];
        if(!flag)continue;
        q[++qc] = now;
    }
    for(int i=0;i<pw[m-k];i++){
        vec now = {};
        int num = i; for(int x=0;x<m-k;x++)now[x] = num%10,num /= 10;
        memset(tmp,0,sizeof tmp); int lim = m+k-1;
        for(int x=k;x<m;x++)for(int y=lim-x;y<m;y++)tmp[x+y] += now[x-k] * now[y-k];
        int flag = 1; for(int x=lim;x<n;x++)flag &= (tmp[x]%10) == z[x];
        if(!flag)continue;
        p[++pc] = now;
    }
    for(int i=1;i<=pc;i++)for(int j=1;j<=qc;j++){
        memset(val,0,sizeof val); memset(tmp,0,sizeof tmp); int cur = m;
        for(int x=m-k-1;x>=0;x--)val[--cur] = p[i][x];
        for(int x=k-1;x>=0;x--)val[--cur] = q[j][x];
        for(int x=0;x<m;x++)for(int y=0;y<m;y++)tmp[x+y] += val[x] * val[y];
        int flag = 1;
        for(int x=0;x<n;x++)flag &= (tmp[x]%10) == z[x];
        if(flag){
            for(int x=m-1;x>=0;x--)cout<<val[x];
            return 0;
        }
    }

    cout<<"-1\n";
    return 0;
}