Problem A - u Calculate e
-------------------------

A simple mathematical formula for e is SUM from 0 to i (1.0 / i!)
where n is allowed to go to infinity.  This can actually yield very
accurate approximations of e using relatively small values of n.
For this problem, you will write a problem that computes the value of
this sequence for various values of n.

Input
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Each line of input will contain one value of n (0 <= n <= 9). The last
line of input will contain -1. This line should not be processed.

Output
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Output the approximation of e generated by the above formula for the
current value of n.  Show no trailing zeroes (and no decimal point for
output with no fractial component), as in the sample output.

Sample Input
------------

1
2
3
-1

Output for Sample Input
-----------------------

2
2.5
2.666666667