spoj#PYTRIP3. Counting Pythagorean Triples
Counting Pythagorean Triples
We define a Pythagorean triple as a set of three positive integers $a$, $b$ and $c$ which satisfy $a^2 + b^2 = c^2$.
Let $P(N)$ denote the number of Pythagorean triples whose hypotenuses ($= c$) are less than or equal to $N$ (i.e. $c \le N$).
Given $N$, find $P(N)$.
Input
The first line of input contains a positive integer $N$.
Output
Print on a single line the value of $P(N)$.
Constraints
$1 \le N \le 1234567891011$
Example
Input1: 5</p>Output1: 1
Input2: 15
Output2: 4
Input3: 10000
Output3: 12471
Input4: 1000000000000
Output4: 4179478903392
Explanation for Input2
There are four Pythagorean triples: $\{3, 4, 5\}$, $\{5, 12, 13\}$, $\{6, 8, 10\}$, $\{9, 12, 15\}$
Information
There are 15 test cases.
The sum of the time limits is 93 sec. (My solution runs in 5.4 sec.)
Source Limit is 5 KB.