#include <fstream>
using namespace std;
ifstream cin ("fact.in") ;
ofstream cout ("fact.out") ;
long a , b , p , n , md , nr , x , put ;
int main()
{

    cin >> p ;
    if ( p==0 )
        cout << 1 ;
    else
    {
        a = 5 ;
        b = 2000000000;
        while ( a <= b )
        {
            md = ( a + b ) / 2 ;
            x = 5 ;
            n = md ;
            put=0 ;
            while ( n / x >= 1 )
            {
                put = put + n/x ;
                x = x*5 ;
            }
            if ( put < p )
                a = md+1;
            else
            {
                if (put == p)
                    nr = md ;
                b = md - 1 ;
            }
        }
        if (nr != 0 )
            cout << nr ;
        else
            cout << "-1" ;
    }
    return 0;
}