#include <iostream>
#include <fstream>

using namespace std;
const int N=2<<31-1;

ifstream in ("fact.in");
ofstream out ("fact.out");

int f(int n)
{
    int nrz=0;
    while (n!=0)
    {
        nrz=nrz+n/5;
        n=n/5;
    }
    return nrz;
}

int search (int p,int st,int dr)
{
    while (st<dr)
    {
    int m=(st+dr)/2;
    if (f(m)<p){st=m+1;search (p,st,dr);}
        else if (f(m)>p){dr=m-1;search (p,st,dr);}
            else if (f(m)==p) return m;

    }
}
int main()
{
    int p;
    in>>p;
    int k=search (p,0,N);
    k=k-k%5;
    out<<k;
    return 0;
}