#include<bits/stdc++.h>
#define rep(i,a,...) for(int i = (a)*(strlen(#__VA_ARGS__)!=0);i<(int)(strlen(#__VA_ARGS__)?__VA_ARGS__:(a));++i)
#define per(i,a,...) for(int i = (strlen(#__VA_ARGS__)?__VA_ARGS__:(a))-1;i>=(int)(strlen(#__VA_ARGS__)?(a):0);--i)
#define foreach(i, n) for(auto &i:(n))
#define pii pair<int, int>
#define pll pair<long long, long long>
#define all(x) (x).begin(), (x).end()
#define bit(x) (1ll << (x))
using ll = long long;
//const ll MOD = (ll)1e9+7;
const ll MOD = 998244353;
const int INF = (ll)1e9+7;
const ll INFLL = (ll)1e18;
using namespace std;
template<class t>
using vvector = vector<vector<t>>;
template<class t>
using vvvector = vector<vector<vector<t>>>;
template<class t>
using priority_queuer = priority_queue<t, vector<t>, greater<t>>;
template<class t, class u> bool chmax(t &a, u b){if(a<b){a=b;return true;}return false;}
template<class t, class u> bool chmin(t &a, u b){if(a>b){a=b;return true;}return false;}
#ifdef DEBUG
#define debug(x) cout<<"LINE "<<__LINE__<<": "<<#x<<" = "<<x<<endl;
#else
#define debug(x) (void)0
#endif

namespace templates{
  ll modpow(ll x, ll b){
    ll res = 1;
    while(b){
      if(b&1)res = res * x % MOD;
      x = x * x % MOD;
      b>>=1;
    }
    return res;
  }

  ll modinv(ll x){
    return modpow(x, MOD-2);
  }

  bool was_output = false;
  template<class t>
  void output(t a){
    if(was_output)cout << " ";
    cout << a;
    was_output = true;
  }
  void outendl(){
    was_output = false;
    cout << endl;
  }
  ll in(){
    ll res;
    scanf("%lld", &res);
    return res;
  }

  template<class t>
  istream& operator>>(istream&is, vector<t>&x){
    for(auto &i:x)is >> i;
    return is;
  }

  template<class t, class u>
  istream& operator>>(istream&is, pair<t, u>&x){
    is >> x.first >> x.second;
    return is;
  }

  template<class t>
  void in(t&x){
    cin >> x;
  }

  template<class t>
  t in(){
    t res; cin >> res; return res;
  }

  template<class t>
  void out(t x){
    cout << x;
  }

  template<class t>
  vector<t> sorted(vector<t> line,function<bool(t,t)> comp=[](t a,t b){return a<b;}){
    sort(line.begin(),line.end(),comp);
    return line;
  }

  template<class t>
  vector<t> reversed(vector<t> line){
    reverse(line.begin(),line.end());
    return line;
  }
}

using namespace templates;

bool func(int w,int h){
  vvector<int> board(w,vector<int>(h,-1));
  per(y,h){
    rep(x,w){
      char d = in<char>();
      if(d=='.'){
        board[x][y] = -1;
      }else{
        board[x][y] = d - '0';
      }
    }
  }

  map<set<pii>,set<pii>> dp;
  int mx[]={-1,0,1,0};
  int my[]={0,1,0,-1};

  auto isin =
    [&](int x,int y){
      return 0<=min(x,y) and x < w and y < h;
    };

  function<set<pii>(int,int)> get_parents =
    [&](int x,int y){
      int color = board[x][y];
      set<pii> current;
      {
        stack<pii> st;
        current.emplace(x,y);
        st.emplace(x,y);
        while(st.size()){
          pii d = st.top();
          st.pop();
          rep(i,4){
            int nx = mx[i] + d.first;
            int ny = my[i] + d.second;
            if(!isin(nx,ny))continue;
            if(color!=board[nx][ny])continue;;
            if(current.count(pii(nx,ny)))continue;
            current.emplace(nx,ny);
            st.emplace(nx,ny);
          }
        }
      }
      if(dp.count(current)){
        return dp[current];
      }
      set<pii> parents;
      foreach(mino,current){
        int nx = mino.first;
        int ny = mino.second+1;
        if(isin(nx,ny) and color != board[nx][ny] and board[nx][ny] >= 0){
          set<pii> d = get_parents(nx,ny);
          foreach(j,d){
            parents.emplace(j);
          }
        }
        parents.emplace(mino);
      }
      dp[current] = parents;
      return parents;
    };
  function<bool(int,int)> check =
    [&](int x,int y){
      set<pii> current;
      int color = board[x][y];
      {
        stack<pii> st;
        current.emplace(x,y);
        st.emplace(x,y);
        while(st.size()){
          pii d = st.top();
          st.pop();
          rep(i,4){
            int nx = mx[i] + d.first;
            int ny = my[i] + d.second;
            if(!isin(nx,ny))continue;
            if(color!=board[nx][ny])continue;;
            if(current.count(pii(nx,ny)))continue;
            current.emplace(nx,ny);
            st.emplace(nx,ny);
          }
        }
      }
      double left = INF;
      double right = -INF;
      foreach(i,current){
        int nx = i.first;
        int ny = i.second - 1;
        if(ny<0 or (board[nx][ny] != color and board[nx][ny] >= 0)){
          left = min(left,nx-0.5);
          right = max(right,nx+0.5);
        }
      }
      set<pii> parents = get_parents(x,y);
      double sum = 0;
      foreach(i,parents){
        sum += i.first;
      }
      sum /= parents.size();
      left += 1e-5;
      right -= 1e-5;
      return left <= sum and sum <= right;
    };
  rep(x,w){
    rep(y,h){
      if(board[x][y]>=0){
        if(!check(x,y)){
          return false;
        }
      }
    }
  }
  return true;
}

int main(){
  int h;
  int w;
  while(true){
    w = in();
    h = in();
    if(!h or !w)break;
    cout << ((func(w,h))?"STABLE":"UNSTABLE") << endl;
  }
  return 0;
}



Measured memory_bytes: 3448