a=int(input())
b=[]


j=0
for i in range(1,a*2,2):
    d=input().split()
    b.append(d[0].split(":"))
    b.append(d[1].split(":"))
    j+=(((1440-int(b[i-1][0])*60-int(b[i-1][1]))+int(b[i][0])*60+int(b[i][1]))%1440)
print(j)