Python: Time Limit Exceeded!

I'm a python developer who's new to competitive programming.

I'm getting TLE for half of the test cases. Can you suggest me some performance improvements in my solution below:

from sys import stdin
 
class Stack(object):
    """ Stack implementation """
    def __init__(self):
        self.elements = []
    def pop(self):
        return self.elements.pop()
    def push(self, item):
        self.elements.append(item)
    def is_empty(self):
        return self.elements == []
    def size(self):
        return len(self.elements)
 
if __name__ == "__main__":

Have you figured it out?

Someone please tell me what's wrong with this logic.

N = int(input())
 
i = 0
 
W = 0
L = -1
 
p1 = 0
p2 = 0
 
while (i < N):
	a, b = raw_input().split()
	p1 += int(a)
	p2 += int(b)
	if p1 > p2:
		diff = p1-p2
		if diff > W:
			W = diff
			L = 1
	else: