ary = []
sum = 0
for i in range(int(input())):
    ary.append([])
    ary[i] = input().split()
    tmp0 = list(map(int, ary[i][0].split(':')))
    tmp1 = list(map(int, ary[i][1].split(':')))
    if(tmp0[0] > tmp1[0]):
        sum += (24 - tmp0[0] - 1) * 60 + (60 - tmp0[1])
        sum += tmp1[0] * 60 + tmp1[1]
    else:
        sum += (tmp1[0] * 60 + tmp1[1]) - (tmp0[0] * 60 + tmp0[1])
        if((tmp1[0] * 60 + tmp1[1]) - (tmp0[0] * 60 + tmp0[1])== -1):
            sum += 24 * 60
print(sum)