import sys

def solve():
    N = int(input())
    M = N // (10**9 + 1)

    ans = kaibun_rekkyo(M)

    print(ans)

def kaibun_rekkyo(n):
    ans = 0

    for l in range(0, 10):
        flag = False

        if l == 0:
            for kai in range(1, 10):
                if kai <= n:
                    # print(kai)
                    ans += 1
                else:
                    flag = True
                    break
        else:
            for a in range(10**(l-1), 10**l):
                kai = a * 10**l + make_rev(a)
                if kai <= n:
                    # print(kai)
                    ans += 1
                else:
                    flag = True
                    break

            for a in range(10**(l-1), 10**l):
                for b in range(0, 10):
                    kai = a * 10**(l+1) + b * 10**l + make_rev(a)
                    if kai <= n:
                        # print(kai)
                        ans += 1
                    else:
                        flag = True
                        break

                if flag:
                    break

        if flag:
            break

    return ans


def make_rev(a):
    res = a % 10
    a //= 10

    while a > 0:
        res = res * 10 + a % 10
        a //= 10

    return res


def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

if __name__ == '__main__':
    solve()