N = int(input())
ans = 0

for i in range(N):
    T,t = map(str,input().split())
    H,M = map(int,T.split(':'))
    h,m = map(int,t.split(':'))
    A = (60*24)-(H*60+M)
    B = h*60+m
    al = (A+B)%(60*24)
    ans += al

print(ans)