#include <iostream>
#include <fstream>
#define NMax 100000000
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int d,s,m,i,j,p,x=-1;
long k;
long nrzero(long n)
{
    long nr=0;
    for(i=5; i<=n; i*=5)
        nr+=n/i;

    return nr;
}
int main()
{
    f>>p;
    if(p==0)
        g<<"1";
    else
    {
        s=1,d=p*5;
        while(s<d)
        {
            m=(s+d)/2;
            k=nrzero(m);
            if(k==p)
                x=m,d=m-1;
            else
            {
                if(k>p)
                    d=m-1;
                else
                    s=m+1;
            }
        }


            g<<x;

    }
    return 0;
}