B.移动（move)

#include<bits/stdc++.h>
using namespace std;
int n,size,a;
long long t;
char c;
int ans;
long long now,step;
bool f=1;
int l[2000001],r[2000001];
int ll,rr;
int nl,nr;
int main() {
    freopen("move.in","r",stdin);
    freopen("move.out","w",stdout);
    cin>>n>>a;
    for(int i=1; i<=n; i++) {
        cin>>c;
        if(c==&#039;#&#039;) {
            ans++;
            if(i<a) {
                ll++;
                l[ll]=i;
            }
            if(i>a) {
                rr++;
                r[rr]=i;
            }
        }
    }
    for(int i=1; i<=(rr+1)/2; i++)
        swap(r[i],r[rr-i+1]);
    while(ans) {
        ans--;
        if(f) {
            if(rr!=0) {
                t+=r[rr]-a;
                a=r[rr];
                f=0;
                rr--;
                continue;
            } else {
                ans++;
                t+=(n+1-a)*2;
                f=0;
                continue;
            }
        } else {
            if(ll!=0) {
                t+=a-l[ll];
                a=l[ll];
                f=1;
                ll--;
                continue;
            } else {
                ans++;
                t+=a*2;
                f=1;
                continue;
            }
        }
    }
    cout<<t;
    return 0;
}