import itertools


def g():
    for d in itertools.count(1):
        for a in range(1, 10):
            for b in range(a+1, 10):
                yield str(a) + str(b)*d


def main():
    N = int(input())
    x = g()
    for i in range(N-1):
        next(x)
    print(next(x))


if __name__ == '__main__':
    main()