from datetime import datetime as dt
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] >= 12):
        ary[i][0] = (24 - tmp0[0] - 1) * 60 + (60 - tmp0[1])
    else:
        ary[i][0] = -(tmp0[0] * 60 + tmp0[1])
    if(tmp1[0] >= 12):
        ary[i][1] = (24 - tmp1[0] -1) * 60 + (60 - tmp1[1])
    else:
        ary[i][1] = tmp1[0] * 60 + tmp1[1]
    sum += ary[i][0] + ary[i][1]
print(sum)