# Task 2: H-Index
# Submitted by: Mohammad S Anwar
# 
# You are given an array of integers containing citations a researcher has received for each paper.
# Write a script to compute the researcher’s H-Index. For more information please checkout the wikipedia page.
# 
#     The H-Index is the largest number h such that h articles have at least h citations each. For example, if an author has five publications, with 9, 7, 6, 2, and 1 citations (ordered from greatest to least), then the author’s h-index is 3, because the author has three publications with 3 or more citations. However, the author does not have four publications with 4 or more citations.
# 
# 
# Example 1
# Input: @citations = (10,8,5,4,3)
# Output: 4
# 
# Because the 4th publication has 4 citations and the 5th has only 3.
# 
# Example 2
# Input: @citations = (25,8,5,3,3)
# Output: 3
# 
# The H-Index is 3 because the fourth paper has only 3 citations.

def main(input)
    if input.length < 1 \
       or \
       input.select{ |i| i[/\D/] }.length > 0
    then
        puts "Input error"
        exit(0)
    end
    output = []
    input.map(&:to_i).sort.reverse.each_with_index { |element, index|
        if element >= index+1
            output.append(element)
        end
    }
    printf "Output: %d\n", output.length
end

main ARGV