#include "cstdio"

#include "string"

#include "cstring"

#include "iostream"

#include "queue"

using namespace std;

struct status

{

    int x,y,dep,key,snake;

    status(int x,int y,int dep,int key,int snake):x(x),y(y),dep(dep),key(key),snake(snake) {}

    bool operator < (const status &a) const {return dep > a.dep;}

};

char map[][];

int n,m,sx,sy,ex,ey,f[][][][],dir[][]={-,,,,,-,,},ans;

void bfs(int x,int y)

{

    priority_queue<status> Q;

    Q.push(status(x,y,,,)) ;

    f[x][y][][]=;

    bool flag=false;

    while(!Q.empty())

    {

        if(flag) break;

        status t=Q.top();Q.pop();

        for(int s=;s<;s++)

        {

            int X=t.x+dir[s][],Y=t.y+dir[s][],key=t.key,snake=t.snake,dep=t.dep;

            if(X<||X>n||Y<||Y>n||map[X][Y]=='#') continue;

            if(isdigit(map[X][Y]))

            {

                int k=map[X][Y]-'';

                if(k==t.key+) key++;

            }

            if(islower(map[X][Y]))

            {

                int k=map[X][Y]-'a';

                if(!(snake&(<<k))) {snake=snake|(<<k);dep++;}

            }

            dep++;

            if(f[X][Y][key][snake]) continue;

            f[X][Y][key][snake]=;

            if(X==ex&&Y==ey&&key==m) {flag=true;ans=min(ans,dep);}

            Q.push(status(X,Y,dep,key,snake));

        }

    }

}

int main()

{

    //freopen("in.txt","r",stdin);

    ios::sync_with_stdio(false);

    string tt;

    while(cin>>n>>m&&n)

    {

        int snake_cnt='a';

        memset(f,,sizeof(f));

        ans=<<;

        for(int i=;i<=n;i++)

        {

            cin>>tt;

            for(int j=;j<tt.size();j++)

            {

                map[i][j+]=tt[j];

                if(tt[j]=='K') {sx=i;sy=j+;}

                if(tt[j]=='T') {ex=i;ey=j+;}

                if(tt[j]=='S') map[i][j+]=snake_cnt++;

            }

        }

        bfs(sx,sy);

        if(ans==<<) cout<<"impossible"<<endl;

        else cout<<ans<<endl;

    }

}