#include <iostream>
#include <fstream>
using namespace std;

int factorial(int n)
{
    if(n <= 1)
        return 1;
    return n * factorial(n - 1);
}

int cate0(int n)
{
    int c = n, k = 0;
    while(c > 1)
    {
        if(c % 10 == 0)
            k++;
        else
            break;

        c /= 10;
    }
    return k;
}
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    long long p;
    int n = 1;
    in>>p;
    while(cate0(factorial(n)) <= p)
    {
        if(cate0(factorial(n)) == p)
            break;
        n++;
    }
    out<<n;
    out.close();
    in.close();
    return 0;
}