import sys
input = sys.stdin.readline

N, M = map(int, input().split())
intervals = []
for _ in range(M):
    A, B = map(int, input().split())
    A -= 1
    B -= 1
    intervals.append((A, B))
intervals.sort(key=lambda p: p[1])
ans = 2*(N-1)
ma = -1
for l, r in intervals:
    if ma <= l:
        ans -= 1
        ma = r
print(ans)