input()

prefs = { "11": 0 }
for c in input():
	nxt_prefs = { "11": 2**32, "01": 2**32, "10": 2**32 }
	for k in prefs:
		nxtk, nxtv = k[1]+"1", prefs[k] + (1 if c == "0" else 0)
		nxt_prefs[nxtk] = min(nxt_prefs[nxtk], nxtv)
		if c == "0" and k == "11":
			nxtk, nxtv = "10", prefs[k]
			nxt_prefs[nxtk] = min(nxt_prefs[nxtk], nxtv)
	prefs = nxt_prefs

print(min(*prefs.values()))