Given letters, probabilities, and transitional probabilities, implement Markov Chain.

Input: `n`

number of transitions

Output: sequence of letters

Letter Probability

...... ........

a 94%

b 2%

c 2%

d 2%

Transition Probability

.......... .............

a->a 25%

a->b 25%

a->c 25%

a->d 25%

b->a 80%

b->b 10%

b->c 5%

b->d 5%

c->a 80%

c->b 10%

c->c 5%

c->d 5%

d->a 80%

d->b 10%

d->c 5%

d->d 5%

Example:

`chain(1)`

--> `a`

`chain(2)`

--> `ab`