import sys
input = sys.stdin.readline

N=int(input())
S=list(input().strip())

ANS=0

for i in range(N):
    if i-1>=0 and S[i]==S[i-1]=="0":
        ANS+=1
        S[i]="1"
    elif i-2>=0 and S[i]==S[i-2]=="0":
        ANS+=1
        S[i]="1"

print(ANS)