>>459 Ruby 0.015秒くらい

[132, 743, 54321, 2147483647, 4294967296].each{|n| puts "n = %d => #%d" % [n, (1..log(n, 5)).map{|i| n / 5**i}.sum]}

# output
n = 132 => #32
n = 743 => #183
n = 54321 => #13576
n = 2147483647 => #536870902
n = 4294967296 => #1073741816