class MyClass:
    patternCount = 0

    def skip(self, maxNum, currentIndex):
        if currentIndex >= maxNum or currentIndex in brokenIndexList:
            return
        
        if maxNum -1 == currentIndex:
            self.patternCount += 1
            return

        self.skip(maxNum, currentIndex + 1)
        self.skip(maxNum, currentIndex + 2)

maxNum, brokenCount= map(int, input().split())

brokenIndexList = []
for i in range(brokenCount):
    brokenIndexList.append(int(input()))

if maxNum == 0:
    print(0)

c = MyClass()
c.skip(maxNum, -1)

print(c.patternCount)
