#include <iostream>
#include <fstream>

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

int nzero(int p)
{
    int fact5 = 5, ans = 0;
    while(fact5 <= p)
    {
        ans += p / fact5;
        fact5 *= 5;
    }

    return ans;
}


int main()
{
    int p;

    fin >> p;

    int st = 0, dr = 1e8 + 5, sol = -1;
    while(st < dr)
    {
        int mij = (st + dr) / 2;

        if(nzero(mij) >= p)
        {
            sol = mij;
            dr = mij;
        }
        else
            st = mij + 1;
    }

    if(p == 0)
        fout << 1;
    else
        fout << sol;

    return 0;
}