#include <iostream>
#include <fstream>

#define Nmax 1000000005

using namespace std;

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

int Solution = -1, n, st, dr, mid;

int Number_of_Zeros(int Number)
{
    int zeros = 0;
    for(int k = 5; Number / k; k *= 5)
        zeros += Number / k;
    return zeros;
}

int main()
{
    fin >> n;
    st = 1;
    dr = Nmax;
    while( st <= dr )
    {
        mid = st + (dr - st) / 2;
        int number = Number_of_Zeros(mid);
        if(number == n)
        {
            Solution = mid;
            dr = mid - 1;
        }
        else if(number < n)
            st = mid + 1;
        else
            dr = mid - 1;
    }
    fout << Solution;
    return 0;
}