import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

n = ni()
s = input()
inf = 10 ** 18
dp = [inf, inf, inf]
dp[0] = 0

for i in range(n):
    if s[i] == "1":
        ndp = [min(dp[0], dp[1]), dp[2], inf]
    else:
        ndp = [min(dp[0] + 1, dp[1] + 1), dp[2] + 1, dp[0]]
    dp = ndp
    # print(dp)
print(min(dp))