import sys
input = sys.stdin.readline

def main():
    N = int(input())
    S = input().strip()

    INF = 10**18
    dp = {(1, 1): 0}

    for c in S:
        ndp = {}
        for (l2, l1), cost in dp.items():
            for out, add in ((0, 0), (1, 1)) if c == '0' else ((1, 0),):
                if l1 == 0 and out == 0:
                    continue
                if l2 == 0 and l1 == 1 and out == 0:
                    continue

                nc = cost + add
                key = (l1, out)
                if nc < ndp.get(key, INF):
                    ndp[key] = nc

        dp = ndp

    ans = min(dp.values())
    print(ans)

if __name__ == "__main__":
    main()