#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int p,st,dr,mij,rez=-1;
int NrZerouri (int x)
{
    int nr = 0;
    for ( int i=5; i <= x; i*=5)
        nr = nr + x/i;
    return nr;
}
int main()
{
    f >> p;
    if ( p == 0 )
        g << 1;
    else
        {

        st = 1; dr = 1000000000;
        while ( st <= dr )
        {
            mij = ( dr - st )/2 + st;
            if ( NrZerouri(mij) == p )
                {
                    rez = mij;
                    dr = mij - 1;
                }
            else if ( NrZerouri(mij) > p )
                    dr = mij - 1;
            else
                if ( NrZerouri(mij) < p )
                    st = mij + 1;

        }
        g << rez;
        }
    return 0;
}