n=int(input())
s=list(input())
ans=0
for i in range(n-1):
    if s[i]=="0":
        if s[i+1]=="0":
            s[i+1]="1"
            ans+=1
        if i!=(n-2) and s[i+2]=="0":
            s[i+2]="1"
            ans+=1
print(ans)