#!/usr/bin/env python3



content = open('input', 'r').readlines()
depth_inc = 0
last_window = 9999
window = [] # queue for "search window"
window_size = 3

while len(window) < window_size:
    window.append(int(content.pop(0).strip()))
# we now have our starting state
last_window = sum(window)
while(content):
    # slide window 1 position
    window.pop(0)
    window.append(int(content.pop(0).strip()))
    window_sum = sum(window)
    if window_sum > last_window:
        depth_inc += 1
    last_window = window_sum
print(depth_inc)