#include <iostream>
#include <fstream>

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

int main()
{
    int p, n, p5, ci;

    fin>>p;
    n = 0;
    while(p5 != p)
    {
        p5 = 0;
        for(int i = 1; i<=n; i++)
        {
            ci = i;
            while(ci % 5 == 0)
            {
                p5 = p5 + 1;
                ci = ci/5;
            }
        }
        n = n + 1;
    }

    fout<<n-1<<endl;
}