#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int aflare(int n)
{
    int put = 5, nr = 0;
    while(put <= n)
    {
        nr += (n / put);
        put = put * 5;
    }
    return nr;
}
int cautbin(int p)
{
    int st = 1, dr = 500000000, rez = -1;
    while(st <= dr)
    {
        int mid = (st + dr) / 2;
        if(aflare(mid) >= p)
            dr = mid - 1, rez = mid;
        else
            st = mid + 1;
    }
    return rez;
}
int main()
{
    int p;
    in >> p;
    out << cautbin(p);
    return 0;
}