The problem is from codeforces: http://codeforces.com/problemset/problem/200/B
This is another easy problem as long as you figure out how to compute the value. For example,
The answer = 
Python gives two lines of solution.
#!/usr/bin/env python
n = int(raw_input())
print "%.8f" % (sum([x for x in map(int, raw_input().split(' '))]) / float(n))
–EOF (The Ultimate Computing & Technology Blog) —
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