#include    <iostream>
#include    <fstream>

using namespace std;

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

int p, i, n;

void read()
{
    fin >> p;
}

int result(int n)
{
    int c = 0;
    while(n != 1)
    {
        n = n / 5;
        c += 1;
        if(n < 10 && n > 5) break;
        if(n < 5 && n > 1) break;
    }
    return c;
}
int main()
{
    read();
    i = 1;
    while(1)
    {
        i += 1;
        if(i % 5 == 0)
        {
            n += result(i);
        }
        if(n == p)
            break;
    }
    fout << i;
    return 0;
}