N = int(input())

sum = 0
for _ in range(N):
    st, ed = map(str, input().split(' '))
    stH, stM = map(int, st.split(':'))
    edH, edM = map(int, ed.split(':'))
    sum += ((edH + 23 - stH) if stH > edH else edH - stH - 1) * 60
    sum += edM - stM if stH == edH else 60 - stM + edM
print(sum)