#include <fstream>
#include <math.h>

using namespace std;

#define NMAX 1000

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    long long p,i,j,nr=0,tmp;
    f>>p;
    if (p==0)
        g<<1;
    else
    {
        p*=5;
        tmp=5;
        for (i=2; i<=NMAX; i++)
        {
            tmp*=5;
            for (int j=tmp; j<=p; j+=tmp)
                p-=5;
            if (tmp>p)
                break;
        }
        g<<p;
    }
    return 0;
}