Stuffing Envelopes

Suppose you have 100 distinct letters to be delivered to 100 different addresses. If you place the letters into randomly chosen pre-addressed envelopes, how many letters on average end up in the correct envelope?

Write a class named EnvelopeStuffer that will simulate 100,000 times the random stuffings of 100 letters into 100 envelopes to answer this question.

Sample run:

This program simulates the following situation:
Suppose you have 100 distinct letters to be delivered 
to 100 different addresses.  If you place the letters 
into randomly chosen pre-addressed envelopes, how many 
letters on average end up in the correct envelope?
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After 100000 trials, the average number of envelopes 
with the correct letter placed inside was 0.99446