a = input().split()
l = int(a[0]) + 1
m = int(a[1])
contain = []
for i in range(m):
    b = input().split()
    contain.append(int(b[0]))
    contain.append(int(b[1]))
l = l - contain[1] + contain[0] -1
for i in range(m-1):
    if contain[i+3] < contain[i+1] and contain[i] < contain[i+3] and contain[i] > contain[i+2]:
        l = l - contain[i] + contain[i+2]
    elif contain[i+1] > contain[i+2] and contain[i+1] < contain[i+3] and contain[i] < contain[i+2]:
        l = l - contain[i+3] + contain[i+1]
    elif contain[i+3] < contain[i+1] and contain[i] < contain[i+2]:
        continue
    else:
        l = l - contain[i+4] + contain[i+3] -1
print(l)