N=int(input())
S=input()
#*0,01,11
dp=[0,0,0]
for i in S:
    ndp=[1<<60]*3
    if i=="0":
        ndp[0]=min(ndp[0],dp[2])
        ndp[1]=min(ndp[1],dp[0]+1)
        ndp[2]=min(ndp[2],dp[1]+1)
        ndp[2]=min(ndp[2],dp[2]+1)
    else:
        ndp[1]=min(ndp[1],dp[0])
        ndp[2]=min(ndp[2],dp[1])
        ndp[2]=min(ndp[2],dp[2])
    dp=ndp
print(min(dp))