#include <iostream>
#include <fstream>

using namespace std;

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

short cif( int m, int n )
{
    int c = 0, f = 5;
    while( f <= m )
    {
        c += m/f;
        f *= 5;
    }

    if( c > n )
        return -1;
    return ( c == n );
}

int main()
{
    int n, m = 1;
    fin >> n;
    while( cif(m, n) == 0 )
        ++m;
    if( cif(m, n) == -1 )
        fout << -1;
    else
        fout << m;

    return 0;
}