#include <stdio.h>
#include <assert.h>
#include <math.h>

unsigned long long N;
float X,min=9999999999.9;

int somma(int x)
{
 int s=0,log,i,p10=1;

 log=(int)(log10((double)x));
 for(i=0;i<=log;i++)
 {
  s+=(int)(floor( ((double)x) / ((double)p10) )) % 10;
  p10*=10;
 }

 return s;
}


int main() {
    FILE *fr, *fw;
    int sqr,x=-1,i;


    fr = fopen("input.txt", "r");
    fw = fopen("output.txt", "w");
    assert(1 == fscanf(fr, "%llu", &N));

    sqr=(int)floor(sqrt(N));
    for(i=0;i<=90;i++)
    {
     X=(sqrt(i*i+4*N)-i)/2.0;
     //fprintf(fw, "i:%d, somma(X):%d, X:%f, (int)X:%d, del:%d\n",i,somma(X),X,(int)X,i*i+4*N);
     //if(X==(int)X) fprintf(fw, "1ok\n");
     //if(somma(X)==i) fprintf(fw, "2ok\n");
     //if(X<min) fprintf(fw, "3ok\n");
     if((X==floor(X))&&(somma(X)==i))
     {
      if(X<min)
      {
       min=X;
       x=X;
       //fprintf(fw, "yep\n");
      }
     }
    }

    fprintf(fw, "%d\n", x);
    fclose(fr);
    fclose(fw);
    return 0;
}