def main():
    N = int(input())
    total = 0
    for x in range(N):
        S1, S2 = input().split()
        H, M = map(int, S1.split(':'))
        h, m = map(int, S2.split(':'))
        
        if H > h or (H == h and M > m):
            h += 24
        
        total += h*60 + m - (H*60 + M)
    print(total)

if __name__ == '__main__':
    main()