#include <fstream>
#include <iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int get_nr_zerouri(int fact_n)
{
    int nr=0;
    for(int p=5;p<=fact_n;p=p*5) // proprietate factori primi
    {
        nr += fact_n/p;
    }
    return nr;
}

int caut_binara(int p) // cauta nr cu p zerouri
{
    int st,dr,m,sol,x;
    st = 1;
    dr = 10000000;
    if(p==0)
        return 1;
    sol = -1;
    while(st<=dr)
    {
        m=st+(dr-st)/2;
        x = get_nr_zerouri(m);
        if(x==p)
        {
            sol=m;
            dr=m-1;
        }
        else if(x>p)
            dr = m-1;
        else if (x<p)
            st = m+1;
    }
    return sol;
}

int main()
{
    int p;
    f>>p;
    g << caut_binara(p);
    return 0;
}