N=int(input())
S=input()
inf = 10**18
dp=[[inf,inf,inf] for _ in range(N+1)]
dp[0][0]=0
for i in range(N):
    if S[i]=="0":
        dp[i+1][0]=min(dp[i][0],dp[i][1])+1
        dp[i+1][1]=dp[i][2]+1
        dp[i+1][2]=dp[i][0]
    else:
        dp[i+1][0]=min(dp[i][0],dp[i][1])
        dp[i+1][1]=dp[i][2]
print(min(dp[-1]))