#include <iostream>
#include <fstream>

using namespace std;

int i,n,j,k,p;
int main()
{
    j=1;
    n=1;
    ifstream f("fact.in");
    f>>p;
    for(i=1;i<=n;i++)
    {
        n=n+1;
        j=j*i;
        while(j%10==0)
        {
            k=k+1;
            j=j/10;
        }
        if(k<=p)
            {
                if(k==p)
                {
                ofstream g("fact.out");
                g<<i;
                return 0;
                }
            }
            else
            {
                    ofstream g("fact.out");
                    g<<-1;
                    return 0;


            }

    }



}