timedata=[]
N=int(input())
for H in range(N):
    a=list(map(int,input().replace(":"," ").split()))
    timedata.append(a)

def dt(a):
    i=0
    if(a[1]>a[3]):
        a[0]+=1
    while(True):
        if(a[1]==a[3]):
            dm=i
            i=0
            break
        a[1]=(a[1]+1)%60
        i+=1

    while(True):
        if(a[0]==a[2]):
            dh=i
            i=0
            break
        a[0]=(a[0]+1)%24
        i+=1
    return dm+dh*60

sum=0
for i in range(N):
     sum+=dt(timedata[i])
print(sum)