#include<bits/stdc++.h>

using namespace std;

template <typename T>
class flow_graph {
 public:
  static constexpr T eps = (T) 1e-9;
 
  struct edge {
    int from;
    int to;
    T c;
    T f;
  };
 
  vector<vector<int>> g;
  vector<edge> edges;
  int n;
  int st;
  int fin;
  T flow;
 
  flow_graph(int _n, int _st, int _fin) : n(_n), st(_st), fin(_fin) {
    assert(0 <= st && st < n && 0 <= fin && fin < n && st != fin);
    g.resize(n);
    flow = 0;
  }
 
  void clear_flow() {
    for (const edge &e : edges) {
      e.f = 0;
    }
    flow = 0;
  }
   
  int add(int from, int to, T forward_cap, T backward_cap) {
    assert(0 <= from && from < n && 0 <= to && to < n);
    int id = (int) edges.size();
    g[from].push_back(id);
    edges.push_back({from, to, forward_cap, 0});
    g[to].push_back(id + 1);
    edges.push_back({to, from, backward_cap, 0});
    return id;
  }
};
 
template <typename T>
class dinic {
 public:
  flow_graph<T> &g;
 
  vector<int> ptr;
  vector<int> d;
  vector<int> q;
 
  dinic(flow_graph<T> &_g) : g(_g) {
    ptr.resize(g.n);
    d.resize(g.n);
    q.resize(g.n);
  }
 
  bool expath() {
    fill(d.begin(), d.end(), -1);
    q[0] = g.fin;
    d[g.fin] = 0;
    int beg = 0, end = 1;
    while (beg < end) {
      int i = q[beg++];
      for (int id : g.g[i]) {
        const auto &e = g.edges[id];
        const auto &back = g.edges[id ^ 1];
        if (back.c - back.f > g.eps && d[e.to] == -1) {
          d[e.to] = d[i] + 1;
          if (e.to == g.st) {
            return true;
          }
          q[end++] = e.to;
        }
      }
    }
    return false;
  }
   
  T dfs(int v, T w) {
    if (v == g.fin) {
      return w;
    }
    int &j = ptr[v];
    while (j >= 0) {
      int id = g.g[v][j];
      const auto &e = g.edges[id];
      if (e.c - e.f > g.eps && d[e.to] == d[v] - 1) {
        T t = dfs(e.to, min(e.c - e.f, w));
        if (t > g.eps) {
          g.edges[id].f += t;
          g.edges[id ^ 1].f -= t;
          return t;
        }
      }
      j--;
    }
    return 0;
  }
 
  T max_flow() {
    while (expath()) {
      for (int i = 0; i < g.n; i++) {
        ptr[i] = (int) g.g[i].size() - 1;
      }
      T big_add = 0;
      while (true) {
        T add = dfs(g.st, numeric_limits<T>::max());
        if (add <= g.eps) {
          break;
        }
        big_add += add;
      }
      if (big_add <= g.eps) {
        break;
      }
      g.flow += big_add;
    }
    return g.flow;
  }
 
  vector<bool> min_cut() {
    max_flow();
    vector<bool> ret(g.n);
    for (int i = 0; i < g.n; i++) {
      ret[i] = (d[i] != -1);
    }
    return ret;
  }
};

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	int n,m;
	cin >> n >> m;
	vector<string> s(n);
	int st,ed;
	int S = m + n;
	int T = S + 1;
	flow_graph<int> f(T+1,S,T);
	dinic<int> d(f);
	int oo = (int)2e7;
	for (int i = 0;i < n;++i) {
		cin >> s[i];
		for (int j = 0;j < m;++j) {
			if (s[i][j] == '.') continue;
			f.add(i,n+j,1,1);
			if (s[i][j] == 'S') {
				f.add(S,i,oo,0);
				f.add(S,n+j,oo,0);
			}
			if (s[i][j] == 'T') {
				f.add(i,T,oo,0);
				f.add(n+j,T,oo,0);
			}
		}
	}
	int ans;
	if ((ans = d.max_flow()) >= oo) cout <<"-1";else cout << ans;
}

Measured memory_bytes: 892