#include <fstream>

using namespace std;
ifstream cin ("fact.in") ;
ofstream cout ("fact.out") ;
int form ( int n )
{
    int cnt = 0 ;
    for ( int i = 5 ; i <= n ; i *= 5 )
        cnt += n / i ;
    return cnt ;
}

int main()
{
    int  P ;
    cin >> P ;
    int i = 1 ;
    while ( 1 )
    {
        if ( form ( i ) == P )
        {
            cout << i ;
            return 0 ;
        }
        else if ( form ( i ) > P )
        {
            cout << -1 ;
            return 0 ;
        }
        i ++ ;
    }

    return 0;


}