#include<iostream>
#include <cmath>
using namespace std;

void x(int *a)
{

    int i1=0;
    int f1=*a;
    int s1=0;
    int c1=0;
    int a3=*a;
    int f=*a;
    while (*a!=0)
    {

        ++i1;
        c1=*a%10;
        *a/=10;

    }


    do
    {
        int k=pow(10,i1);
        s1+=f1/k;
        f1%=k;

        --i1;
    } while (i1!=0);
    int a2=s1+f%10;
    int a1=a2/10+a2%10;
    if (a1>10) {
        a1/=2;
        a2-=a1;
    }
    else {


        if (a1==a2 && a1) {
            *a=a3+a1;
        }else {
            *a=a3+a2+a1;

        }
    }

}

int main() {


    int b=0;
    cin>>b;
    if (b<10)
    {
        cout<<b;
    }
    else if (b<=10)
    {
        cout<<-1;
    }else
    {

        for (int i=b;i>=floor(b/1.5);--i)
        {
            int g=i;
            x(&g);


            if (g==b)
            {
                cout<<i;
                break;
            }
            else if (i==floor(b/1.5) && g!=b)
            {
                cout<<-1;
                break;
            }
        }
    }

    return 0;
}