# 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.

import re
import sys

if __name__ == "__main__":
    input = sys.argv[1:]
    if (len(input) < 1
        or
        len(list(filter(lambda x: re.search(r'\D', x), input))) > 0):
        sys.exit("Input error")

    input = sorted(list(map(int, input)), reverse=True)
    print("Output: {:d}".format(len([i for i in range(len(input)) if input[i] >= i+1])))