#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
unsigned long p, gasok, li=0,ls=2000000000,mijd, m, n;

int main()
{
    fin >> p;
    if( p==0 )
    {
    fout <<"1"<<endl;
    return 0;
    }
    while( li <= ls && !gasok )
    {
        mijd = li / 2 + ls / 2;
        n = mijd;
        m=0;
        while( n != 0 )
        {
            m += n / 5;
            n /= 5;
        }
        if( m == p ) gasok = mijd;
        else if( m < p )
            li = mijd + 1;
        else ls = mijd - 1;
    }

    if (!gasok) fout<<"-1"<<endl;
    else
    fout<<gasok-gasok%5<<endl;
    return 0;
}