import collections
from decimal import Decimal
import heapq
import sys
import math
import itertools
import bisect
from io import BytesIO, IOBase
import os
from unicodedata import decimal
def valid(i,j,n,m):
if i<n and i>=0 and j>=0 and j< m :return True return False
def sumn(i,n):
return (n-i)*(i+n)/2
def sqfun(a,b,c):
return (-b+math.sqrt(b*b-4*a*c))/2*a
def getprime(num):
if all(num%i!=0 for i in range(2,int(math.sqrt(num))+1)):return True
def value(): return tuple(map(int, input().split()))
def values(): return tuple(map(int, sys.stdin.readline().split()))
def inlst(): return [int(i) for i in input().split()]
def inlsts(): return [int(i) for i in sys.stdin.readline().split()]
def inp(): return int(input())
def inps(): return int(sys.stdin.readline())
def instr(): return input()
def stlst(): return [i for i in input().split()]
def solve():
n=inp()
for sm in range(1,91):
sx = (Decimal((sm**2)+4*n).sqrt()-sm)/2
if sx>0 and int(sx)==sx:
if sm==sum([int(i) for i in str(int(sx))]):
return int(sx)
return -1
if __name__ == "__main__":
print(solve())
#include<bits/stdc++.h>
using namespace std;
#define AYAALI ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define FOR(i, a, b) for(int i = int(a); i < int(b); i++)
#define yes cout<<"YES\n";
#define no cout<<"NO\n";
#define ll long long
#define pb(x) push_back(x)
#define MP(x, y) make_pair(x,y)
#define fi first
#define se second
#define endl '\n'
#define all(v) v.begin(), v.end()
const double EPS = 1e-9;
const ll N=1e5+1;
//---------------------------------------------
/*void files(){
freopen("pails.in", "r", stdin);
freopen("pails.out", "w", stdout);
}*/
ll s(ll i){
ll sum=0;
// 99
while(i>0){
sum+=(i%10);
i/=10;
}
return sum;
}
void solve()
{
ll n;
cin>>n;
ll ans=0;
// x biggest val 10^9 biggest sum 999999999
// 1.53 - 1 = 0.53 *10 = 5.3
for(ll i =1;i<=100;i++){
ll in = (-i+sqrt(pow(i,2)+(4*n)))/2;
double de = (-i+sqrt(pow(i,2)+(4*n)))/2;
if(in>0 && (de-in)*1000000000==0 ){
if(i == s((-i+sqrt(pow(i,2)+(4*n)))/2)){ans=(-i+sqrt(pow(i,2)+(4*n)))/2;break;}
}
}
if(ans)cout<<ans;
else cout<<-1;
}
int main() {
AYAALI
ll t=1;
//files();
//cin>>t;
while(t--){
solve();}
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