class letterCount {
    public static void main(String[] args) {
        int[] base = new int[10];
        for(int i = 0; i < 10; i++) {
            base[i] = -1;
        }
        long ret = getCount(base, 7);
        System.out.println(ret);
    }
    private static boolean inArray(int needle, int[] haystack) {
        for(int i : haystack) {
            if(i == needle) {
                return true;
            }
        }
        return false;
    }
    private static long getCount(int[] base, int maxrec) {
        long count = 0;
        int last = -1;
        int curcount = 0;
        int[] tbase = new int[10];
        for(int j : base) { //Get length of array and last letter in it
            if(j == -1) {
                break;
            }
            else {
                last = j;
                curcount += 1;
            }
        }
        for (int i=0; i<26; i++) {
            if(inArray(i, base)) {
                continue;
            }
            if(last != -1 && i != 0 && last == (i - 1)) {
                continue;
            }
            else {
                System.arraycopy(base, 0, tbase, 0, 10);
                tbase[curcount] = i;
                if(curcount == (maxrec - 1)) {
                    count += 1;
                }
                else {
                    count += getCount(tbase, maxrec);
                }
            }
        }
        return count;
    }
}