import sys

n = input()

arr = bytearray(n)
i = 0

while i < n:
    line = raw_input().split()
    arr[i] = (int(line[0]) + int(line[1]))
    i += 1

result = ""

i = n-1
while i > 0:
    if arr[i] > 9:
        arr[i] -= 10
        arr[i-1] += 1
    result = str(arr[i]) + result
    i -= 1

arr[0] = arr[0]%10
result = str(arr[0]) + result

print result

result = str(arr[i]) + result

Run this code 1M iterations locally.