N = int(input())
S = list(map(int,list(input())))
ans = 0
if S[0]==S[1]==0:
    S[1] = 1
    ans += 1
for i in range(2,N):
    if S[i-2:i+1].count(0)>S[i-1:i+1].count(1):
        S[i] = 1
        ans += 1
print(ans)