#include <fstream>

using namespace std;

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

int Verf(int mij)
{
    int nr5 = 0;//24
    while(mij != 0)
    {
        nr5=nr5+mij/5;
        mij=mij/5;

    }
    return nr5;
}

int main()
{
    int n, st, dr, mij, rez, sol, rest;
    fin >> n;
    st = 0;
    dr = 500000000;
    while(st <= dr)
    {
        mij = (st + dr) / 2;
        rez = Verf(mij);
        if(rez == n)
        {
            sol = mij;
            break;
        }
        else
            if(rez < n) st = mij + 1;
            else dr=mij-1;
    }
    rest = sol % 5;
    fout << sol - rest;


    return 0;
}