n=int(input())
data=[input().split() for i in range(n)]
t=0
for i in range(n):
    d_1=data[i][0].split(":")
    d_2=data[i][1].split(":")
    H=int(d_1[0])
    M=int(d_1[1])
    h=int(d_2[0])
    m=int(d_2[1])
    if h>H:
        t+=(60-M)%60+m+(h-H-1)*60
    elif h==H:
        if m>=M:
            t+=m-M
        else:
            t+=24*60-M+m
    else:
        t+=60*h+m+24*60-60*H-M
print(t)