"""

00
010
を避ける

"""

N = int(input())

S = input()

# 01,10,11
dp = [0,0,0]

for i in range(N):

    ndp = [float("inf")] * 3
    
    if S[i] == "1":
        ndp[0] = dp[1]
        ndp[2] = min(dp[0], dp[2])

    else:
        ndp[0] = dp[1]+1
        ndp[1] = dp[2]
        ndp[2] = min(dp[0], dp[2]) + 1

    dp = ndp

print (min(dp))