INF = float("inf")
n = int(input())
s = list(map(int, input()))
dp = [[INF, INF, INF] for _ in range(n+1)] # normal, 0, 01
dp[0][0] = 0
for i in range(n):
    if s[i] == 1:
        dp[i+1][0] = min(dp[i+1][0], dp[i][0])
        dp[i+1][0] = min(dp[i+1][0], dp[i][2])
        dp[i+1][2] = min(dp[i+1][2], dp[i][1])
    else:
        dp[i+1][0] = min(dp[i+1][0], dp[i][0]+1)
        dp[i+1][1] = min(dp[i+1][1], dp[i][0])
        dp[i+1][2] = min(dp[i+1][2], dp[i][1]+1)
        dp[i+1][0] = min(dp[i+1][0], dp[i][2]+1)
        
# print(*dp, sep="\n")
print(min(dp[n]))