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

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

int p, i=0;

int fact(int a)
{
    int f;

    if(a <= 1)
        return 1;

    f = a * fact(a-1);

    return f;
}

int zero(int a)
{
    int z = 0;

    while(!(a % 10))
    {
        a /= 10;
        z++;
    }

    return z;
}

int main()
{
    fin >> p;

    while(p)
    {
        if(p == zero(fact(i)))
            break;
        i++;
    }

    fout << i;

    return 0;
}