#include<stdio.h>
char s[200005];
int main()
{
	int n;
	scanf("%d", &n);
	scanf("%s", s);
	int sum = 0, ans = 0, max = -1e9;
	int i;
	for (i = 0; i < n; i++)
	{
		if (s[i] == '0')
		{
			sum--;
			if (sum - max < 0)
			{
				ans++;
				sum += 2;
			}
			if (max < sum)
				max = sum;
		}
		else
			sum++;
	}
	printf("%d\n", ans);
	return 0;
}