n = int(input())
s = input()

count0 = 0
count1 = 0
operations = 0

for c in s:
    if c == '0':
        count0 += 1
    else:
        count1 += 1

    if count0 > count1:
        operations += 1
        count0 -= 1  # この0を1に変えたと仮定

print(operations)