#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

int log5(int a)
{
    int i,sol=0;
    for(i=1;i<=a;i*=5)
    {
        sol++;
    }
    return sol;
}

int main()
{
    unsigned long long p;
    in>>p;
    if(p==0)
        out<<1;
    else
        out<<5*(p-log5(p)+1);
    return 0;
}