#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    int x,p,y,i,j,nr;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>p;
    x=5*p;
    y=p;

    if (p==0)
        g<<1;
    else
    {
        for (i=5;i<=y;i+=5)
        {
            j=i;
            while (j%5==0)
            {
                j=j/5;
                x-=5;
                y--;
            }
        }
        g<<x;
  }

    return 0;
}