#include<bits/stdc++.h>
// #pragma optimize("-O3")
//  #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,avx,mmx,tune=native")
using namespace std;
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define INF 1e9
//#define BIG_INF 1e18
#define vi vector<ll>
#define sz(a) ll((a).size())
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1)
// #include <ext/pb_ds/assoc_container.hpp> // Common file
// #include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
// typedef tree<
// ll,
// null_type,
// less<ll>,
// rb_tree_tag,
// tree_order_statistics_node_update>
// ordered_set;
typedef long long ll;
 const ll BIG_INF = 3e18;
ll mod = 1e9+7;
 ll fast_exp(ll a, ll b)
{
    if(b <= 0)
       return 1;
    else
    {
       ll res = 1;
       res = fast_exp(a,b/2);
       res = (res*res)%mod;
       if(b%2 == 1)
          res = (res*a)%mod;
       return res;
 
    }
}

typedef long double ld;
const long long N = 1e5+1000;
const long double pi = acos(-1.0);
using cd = complex<double>;
const double PI = acos(-1);

int par[2][N] = {};
int comp[2] = {};

int find_par(int v, int mode)
{
    if(par[mode][v] == v)
        return v;
    else 
        return par[mode][v] = find_par(par[mode][v],mode);
}

void union_find(int a, int b, int mode)
{
    a = find_par(a,mode);
    b = find_par(b,mode);
    if(a != b)
    {
        par[mode][a] = b;
        comp[mode]--;
    }
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    //freopen("input.txt","r",stdin);
    int h, w;
    cin >> h >> w;
    char a[h][w] = {};
    for(int i = 0; i<h; i++)
        for(int j = 0; j<w; j++)
        {
            cin >> a[i][j];
        }
        a[0][0] = '#';
        a[h-1][0] = '#';
        a[0][w-1] = '#';
        a[h-1][w-1] = '#';
    for(int i = 0; i<h; i++)
        par[0][i] = i;
    comp[0] = h;
    for(int i = 0; i<w; i++)
        par[1][i] = i;
    comp[1] = w;

    for(int category = 0; category < w; category++)
    {
        int prev = -1;
        for(int i = 0; i<h; i++)
        {
            if(a[i][category] == '#')
            {
                if(prev == -1)
                    prev = i;
                else
                {
                    union_find(prev,i,0);
                    prev = i;
                }
            }
        }
    }

    for(int category = 0; category < h; category++)
    {
        int prev = -1;
        for(int i = 0; i<w; i++)
        {
            if(a[category][i] == '#')
            {
                if(prev == -1)
                    prev = i;
                else
                {
                    union_find(prev,i,1);
                    prev = i;
                }
            }

        }
    }

    int ans = min(comp[0],comp[1]);
    ans--;
    cout << ans << '\n';




    // cerr<< '\n' << "Time elapsed :" << clock() * 1000.0 / CLOCKS_PER_SEC << " ms\n" ;
    return 0;
    
    
}










 
//#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,abm,mmx,avx,avx2,fma,tune=native") 

#include <bits/stdc++.h>

using namespace std ;

#define int int64_t //be careful about this 
#define endl "\n"
#define f(i,a,b) for(int i=int(a);i<int(b);++i)

#define pr pair
#define ar array
#define fr first
#define sc second
#define vt vector
#define pb push_back
#define LB lower_bound  
#define UB upper_bound
#define PQ priority_queue

#define sz(x) ((int)(x).size())
#define all(a) (a).begin(),(a).end()
#define allr(a) (a).rbegin(),(a).rend()
#define mem0(a) memset(a, 0, sizeof(a))
#define mem1(a) memset(a, -1, sizeof(a))

template<class A> void rd(vt<A>& v);
template<class T> void rd(T& x){ cin >> x; }
template<class H, class... T> void rd(H& h, T&... t) { rd(h) ; rd(t...) ;}
template<class A> void rd(vt<A>& x) { for(auto& a : x) rd(a) ;}

template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }

template<typename T>
void __p(T a) {
  cout<<a; 
}
template<typename T, typename F>
void __p(pair<T, F> a) {
  cout<<"{";
  __p(a.first);
  cout<<",";
  __p(a.second);
  cout<<"}\n"; 
}
template<typename T>
void __p(std::vector<T> a) {
  cout<<"{";
  for(auto it=a.begin(); it<a.end(); it++)
    __p(*it),cout<<",}\n"[it+1==a.end()]; 
}
template<typename T, typename ...Arg>
void __p(T a1, Arg ...a) {
  __p(a1);
  __p(a...);
}
template<typename Arg1>
void __f(const char *name, Arg1 &&arg1) {
  cout<<name<<" : ";
  __p(arg1);
  cout<<endl;
}
template<typename Arg1, typename ... Args>
void __f(const char *names, Arg1 &&arg1, Args &&... args) {
  int bracket=0,i=0;
  for(;; i++)
    if(names[i]==','&&bracket==0)
      break;
    else if(names[i]=='(')
      bracket++;
    else if(names[i]==')')
      bracket--;
  const char *comma=names+i;
  cout.write(names,comma-names)<<" : ";
  __p(arg1);
  cout<<" | ";
  __f(comma+1,args...);
}

void setIO(string s = "") {
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); 
  cin.exceptions(cin.failbit); 
	cout.precision(15);	cout << fixed;
  #ifdef ONLINE_JUDGE
  if(sz(s)){
  	freopen((s+".in").c_str(),"r",stdin);
  	freopen((s+".out").c_str(),"w",stdout);
  }
  #endif
}
const int inf = 1e9, A = 26;
signed main(){
  setIO() ;
  int n,m; rd(n,m);
  int dp[n][n];  
  f(i,0,n) f(j,0,n) dp[i][j] = inf ;
  f(i,0,n) dp[i][i] = 0;
  vt<int> g[n][A];
  f(_,0,m){
  	int u,v; char c;
  	rd(u,v,c); 
  	--u,--v;
  	ckmin(dp[u][v],int(1));
  	ckmin(dp[v][u],int(1));
  	g[u][c-'a'].pb(v);
  	g[v][c-'a'].pb(u);
  }
  PQ<ar<int,3>> q;
  f(i,0,n) f(j,0,n) q.push({-dp[i][j],i,j});
  while(sz(q)){
  	auto a = q.top(); q.pop();
  	int v = -a[0], i = a[1], j = a[2];
  	//if(dp[i][j] != v) continue;
  	f(k,0,A){
  		for(auto x : g[i][k]){
  			for(auto y : g[j][k]){
  				if(ckmin(dp[x][y],v + 2)){
  					q.push({-dp[x][y],x,y});
  				}
  			}
  		} 
  	}
  }
  cout << (dp[0][n-1] == inf ? int(-1) : dp[0][n-1]);
}

