l=int(input())
n=int(input())
a=list(map(int,input().split()))
s=0
m=0
for i in range(n):
    if (a[i]==1) and (a[i-1]!=1) and (a[i-2]!=1):
        m=i
        s=s+1
    elif a[i]==1:
        if i-m+1==l:
            m=0
print(s)