Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
#define LL long long
#define DB long double
using namespace std;
//#define P 998244353
//inline int ad(int x,int y){return (x+y>=P)?(x+y-P):(x+y);}
//inline int mt(int x,int y){return 1ll*x*y%P;}
//inline void mo(int &x){x=(x>=P)?(x-P):x; x=(x<0)?(x+P):x;}
template<typename T>inline void ckmx(T &x,T y){x=max(x,y);}
template<typename T>inline void ckmi(T &x,T y){x=min(x,y);}
template<typename T>void read(T &x){
	x=0;int f=1;
	char c=getchar();
	for(;!isdigit(c);c=getchar()) if (c=='-') f=-1;
	for(;isdigit(c);c=getchar()) x=x*10+c-48;
	x*=f;
}
int n;
string s;
int sb[200010],sw[200010];
int main(){
	read(n); 
	cin>>s;
	for(int i=0;i<n;++i){
		sb[i+1]=sb[i]+(s[i]=='#');
		sw[i+1]=sw[i]+(s[i]=='.');
	}
	int ans=1e9;
	for(int i=0;i<=n;++i)
		ans=min(ans,sb[i]+sw[n]-sw[i]);
	cout<<ans<<endl;
	return 0;
}