/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on February 9, 2010, 11:32 AM
 */
#include <fstream>

/*
 *
 */
using namespace std;
int main( void )
{
    unsigned long long int p, i, j, f=0, nr=0;
    ifstream in("fact.in");
    in>>p;
    for( i=1; ; ++i )
    {
        for( j=i, nr=0; 0 == j%5; ++nr, j/=5 );
        f+=nr;
        if( f == p )
        {
            ofstream out("fact.out");
            out<<i<<'\n';
            return 0;
        }
        if( f > p )
        {
            ofstream out("fact.out");
            out<<-1;
            return 0;
        }
    }
    return 0;
}