public class Euler158 {
    static long binom(int n, int k) {
        if (k < 0 || k > n)
            return 0;
        k = Math.min(k, n - k);
        long r = 1;
        for (int i = 1; i <= k; i++)
            r = r * (n - k + i) / i;
        return r;
    }

    public static void main(String[] args) {
        int alpha = 26;
        long best = 0;
        for (int n = 1; n <= alpha; n++) {
            long e = (1L << n) - n - 1;
            best = Math.max(best, binom(alpha, n) * e);
        }
        System.out.println(best);
    }
}