#include <fstream>
using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
long long p;
long long fact (int p)
{
    long long nr_cinci=0;
    for (int i=5;i<=p;i*=5)
    {
       nr_cinci+=p/i;
    }
    return nr_cinci;
}
int main()
{
    in>>p;
    long long l,g,m;
    l=0;
    g=5*p;
    if(!p) {
        out << "0";
        return 0;
    }
    while (l<g)
    {
        m=(l+g)/2;
        if (fact(m)>=p)
        {
            g=m;
        }
        else
        {
            l=m+1;
        }
    }

    if (fact(l) == p)
        out<<l;
    else out<<g;
    return 0;
}