For some reason, the output is not buffered in PyPy (unlike CPython).
So, for problems where you use lots of print statements (especially in loops), unbuffered output has a significant effect on overall run-time performance.

For example, compare these 2 submissions -- 21354004, 21354013.
Both solutions are exactly the same except in the latter, stdout is replaced by a buffer and all the output stored in the buffer is written to original stdout at the end.

21354004 times out (1000ms TL) even though everything except buffering is same as 21354013.
21354013 runs in 360ms -- at least 3x faster than the unbuffered solution.

For explicit buffered output, prefix your code with following code like in 21354013

import atexit
import io
import sys

buff = io.BytesIO()
sys.stdout = buff


@atexit.register
def write():
    sys.__stdout__.write(buff.getvalue())


# code

Edited template (with unbuffered input), post hellman_'s comment

import atexit
import io
import sys

_INPUT_LINES = sys.stdin.read().splitlines()
raw_input = iter(_INPUT_LINES).next
_OUTPUT_BUFFER = io.BytesIO()
sys.stdout = _OUTPUT_BUFFER


@atexit.register
def write():
    sys.__stdout__.write(_OUTPUT_BUFFER.getvalue())


# code