N = int(input())
ans = 0
for i in range(N) :
    counter = 0
    A,B = map(str,input().split())
    A = list(A.split(":"))
    B = list(B.split(":"))
    if int(B[1])-int(A[1]) < 0 :
        m = int(B[1])-int(A[1]) + 60 
        counter += 1
    else :
        m = int(B[1])-int(A[1]) 
    if int(B[0]) - counter - int(A[0]) < 0 :
        h = int(B[0]) - counter - int(A[0]) + 24
    else :
        h = int(B[0]) - counter - int(A[0])
    ans += h*60 + m
print(ans)