import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N = int(readline())
data = readlines()

answer = 0
for line in data:
    (a,b),(c,d) = [map(int,x.split(b':')) for x in line.split()]
    s = 60 * a + b; t = 60 * c + d
    t -= s
    if t < 0:
        t += 1440
    answer += t

print(answer)