#include <stdio.h>

char x[300010];
int last[300010];
int main()
{
	int a;
	scanf("%d",&a);
	scanf("%s",x+1);
	int p = a+1, ans = 0;
	last[a+1] = -1;
	for(int i=a;i>=1;i--)
	{
		if(x[i]=='#')
		{
			if((a-i)<=last[p]) last[i] = last[p]+2;
			else last[i] = (a+1-i);
			ans = ans>last[i]?ans:last[i];
			p = i;
		}
	}
	printf("%d",ans);
}