n = int(input())
s = list(input())
pre = s[0]
cnt = 0
t = []
for c in s:
	if pre==c:
		cnt += 1 
	else:
		t.append((pre, cnt))
		pre = c
		cnt = 1 
t.append((pre, cnt))
ans = 0
for c, v in t:
	if c=="0":
		ans += v-1
print(ans)