#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N,L;
string S;

void flip(int& cnt,char &tar) {
	cnt-=tar;
	tar^=1;
	cnt+=tar;
}

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>S;
	L=S.size();
	N--;
	FORR(c,S) c=(c=='#');
	ll mi=1LL<<60;
	
	FOR(i,2) {
		string T=S;
		int LL=L+1;
		int cnt=0;
		FOR(j,L) if(S[j]) {
			cnt++;
			LL=min(LL,j);
		}
		
		
		ll tot=0;
		int cur=N;
		
		if(LL<cur) {
			for(j=LL;j<cur;j++) flip(cnt,T[j]);
			tot=cur-LL;
			cur=LL;
		}
		while(cnt) {
			if(T[cur]==0) {
				tot++;
				cur++;
				flip(cnt,T[cur]);
			}
			else {
				tot+=2;
				T[cur]=0;
				cnt--;
				flip(cnt,T[cur+1]);
			}
		}
		
		mi=min(mi,tot);
		reverse(ALL(S));
		N=L-1-N;
	}
	cout<<mi<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}