#include <iostream>
#include <fstream>

using namespace std;

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

int p,k,km,n=1;
int main()
{
    fin>>p;
    if(p==0)fout<<"1";
    else
    {
        for(int i=1;k<p;++i)
        {
            k+=i;
            km-=i;
        }
        if(k==p)fout<<n;
        else{
            if(km==p)fout<<km;
            else fout<<"-1";}

    }

    return 0;
}