import bisect

count = 0

intervals = []

with open("input.txt" , "r") as file:
    for line in file:
        line = line.strip()
        if line == "":
            break
        start, end = map(int, line.split("-"))
        intervals.append((start, end))
    
    intervals.sort(key = lambda x: x[0])
    merged = [intervals[0]]

    for current_start, current_end in intervals[1:]:
        last_start, last_end = merged[-1]
        if current_start <= last_end:
            merged[-1] = (last_start, max(last_end, current_end))
        else:
            merged.append((current_start, current_end))
    
    for interval in merged:
        count += interval[1] - interval[0] + 1

print(count)