with open(r'day5/input.txt', 'r') as input:
    lines = input.read().split('\n')[:-1]

blank = lines.index('')
ranges = [list(map(lambda x: int(x), lines[i].split('-'))) for i in range(blank)]

ranges.sort(key=lambda x: x[0])
sum = 0

while ranges != []:
    maxi = ranges[0][1]
    mini = ranges[0][0]
    ranges.pop(0)
    while ranges != [] and ranges[0][0] <= maxi :
        maxi = max(ranges[0][1],maxi)
        ranges.pop(0)
    sum += maxi-mini +1

print(sum)