#include <bits/stdc++.h>
using namespace std;
#define in ios_base::sync_with_stdio(0); fin.tie(NULL); fout.tie(NULL);
#define out return 0;
#define NMAX 100000000
ifstream fin("fact.in");
ofstream fout("fact.out");
int nr0(int n)
{
    int aux = 5, sol = 0;
    while (aux <= n)
    {
        sol+=n/aux;
        aux*=5;
    }

    return sol;
}
int solve(int n)
{
    if (n == 0)
        return 1;
    int st = 1, dr = NMAX;
    while (st <= dr)
    {
        int mid = st + (dr - st)/2;
        int nr = nr0(mid);
        if (nr == n)
            return mid - mid % 5;
        if (nr < n)
            st = mid + 1;
        else
            dr = mid - 1;
    }
    return - 1;

}
int main()
{
    in
    int n;
    fin >> n;
    fout << solve(n);
    out
}