#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int p,k,km,n=1,minim=0,cop;

int main()
{
    fin>>p;
    if(p==0)break;
    else{


        /*if(n%2==0)while(cop%2==0){k2++;cop/=2;}
        if(n%5==0)while(cop%5==0){k5++;cop/=5;}
        if(k2<k5)minim=k2;
        else minim=k5;
        if(minim==p)break;
        if(n==1||n%10==4)++n;
        else n+=2;*/
        for(int i=1;k<p;+=i)
        {
            k+=i;
            km-=1;
        }
        if(k==p)fout<<n;
        else fout<<"-1"

    }

    return 0;
}