def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    S = input().rstrip()

    
    INF = 10**18
    dp = [[INF]*2 for _ in range(2)]
    
    dp[0][0] = 0

    for i in range(N):
        c = S[i]
        ndp = [[INF]*2 for _ in range(2)]
        for d1 in (0,1):
            for d2 in (0,1):
                cost = dp[d1][d2]
                if cost == INF: continue

                
                nc = '1'
                flip = 1 if c == '0' else 0
        
                nd1, nd2 = 0, d1
                ndp[nd1][nd2] = min(ndp[nd1][nd2], cost + flip)

                if d1 == 0 and d2 == 0:
                    flip = 1 if c == '1' else 0
                    nd1, nd2 = 1, 0
                    ndp[nd1][nd2] = min(ndp[nd1][nd2], cost + flip)

        dp = ndp

    ans = min(dp[d1][d2] for d1 in (0,1) for d2 in (0,1))
    print(ans)


if __name__ == '__main__':
    main()