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] = tmp0[0] * 60 + tmp0[1]
    else:
        ary[i][0] = (12 + tmp0[0]) * 60 + tmp0[1]
    if(tmp1[0] >= 12):
        ary[i][1] = (12 + tmp1[0]) * 60 + tmp1[1]
    else:
        ary[i][1] = tmp1[0] * 60 + tmp1[1]
    sum += ary[i][0] - ary[i][1]
print(sum)