#include<bits/stdc++.h>
 
using namespace std;
 
using ll=long long;
using pp=pair<int,int>;
#define sr string 
#define vc vector
#define db double
#define fi first
#define se second
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define pque priority_queue
#define bpc(a) __builtin_popcount(a)
int main(){
	int n;sr s;cin>>n>>s;
	int ans=-1; int last=-20;
	for(int i=n-1;i>=0;i--)if(s[i]=='#'){
		int now=n-i;
		if(now<=last+1)now=last+2;
		ans=max(ans,now);
		last=now;
		
	}
	cout<<ans;
}