using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using static Template;
using static System.Console;
using static System.Convert;
using static System.Math;
using Pi = Pair<int, int>;
using Number = System.Int64;

class Solver
{
    public void Solve()
    {
        int h, w;
        Input.Make(out h, out w);
        var grid = Input.grid(h);
        Pi s = new Pi(), t = new Pi();
        var f = new MaxFlow(h + w + 2);
        for (var i = 0; i < h; i++)
            for (var j = 0; j < w; j++)
                if (grid[i][j] != '.')
                    f.AddUndirectedEdge(i,j+h, 1);
        for (var i = 0; i < h; i++)
            for (var j = 0; j < w; j++)
                if (grid[i][j] != '.')
                {
                    if (grid[i][j] == 'S')
                    {
                        s = new Pi(i, j);
                        f.AddDirectedEdge(h + w, i, int.MaxValue);
                        f.AddDirectedEdge(h + w, h + j, int.MaxValue);
                    }
                    if (grid[i][j] == 'T')
                    {
                        t = new Pi(i, j);
                        f.AddDirectedEdge(i, h + w + 1, int.MaxValue);
                        f.AddDirectedEdge(h + j, h + w + 1, int.MaxValue);
                    }
                }
        if (s.v1 == t.v1 || s.v2 == t.v2)
            Fail(-1);
        WriteLine(f.Execute(h + w, h + w + 1));
    }
}


public class MaxFlow
{
    readonly List<Edge>[] G;
    readonly int[] lv, iter;

    public MaxFlow(int V)
    {
        G = new List<Edge>[V];
        lv = new int[V];
        iter = new int[V];
        for (int i = 0; i < G.Length; i++)
            G[i] = new List<Edge>();
    }

    public void AddDirectedEdge(int from, int to, int cap)
        => addEdge(from, to, cap, 0);

    public void AddUndirectedEdge(int from, int to, int cap)
        => addEdge(from, to, cap, cap);

    void addEdge(int f, int t, int c1, int c2)
    {
        var a = new Edge(t, c1);
        var b = new Edge(f, c2);
        Edge.Link(a, b);
        G[f].Add(a);
        G[t].Add(b);
    }

    public int Execute(int src, int sink, int f = -1)
    {
        int flow = 0;
        if (f < 0) f = int.MaxValue;
        while (f > 0)
        {
            bfs(src);
            if (lv[sink] == 0) return flow;
            Array.Clear(iter, 0, iter.Length);
            int df;
            while ((df = dfs(src, sink, f)) > 0) { flow += df; f -= df; }
        }
        return flow;
    }

    void bfs(int s)
    {
        Array.Clear(lv, 0, lv.Length);
        var q = new Queue<int>();
        lv[s] = 1;
        q.Enqueue(s);
        while (q.Count > 0)
        {
            var v = q.Dequeue();
            foreach (var e in G[v])
                if (e.Cap > 0 && lv[e.To] == 0)
                {
                    lv[e.To] = lv[v] + 1;
                    q.Enqueue(e.To);
                }
        }

    }
    int dfs(int v, int t, int f)
    {
        if (v == t) return f;
        int ret = 0;
        for (; iter[v] < G[v].Count; iter[v]++)
        {
            var e = G[v][iter[v]];
            if (e.Cap <= 0 || lv[v] >= lv[e.To]) continue;
            int df = dfs(e.To, t, Math.Min(f, e.Cap));
            if (df <= 0) continue;
            e.Cap -= df;
            e.Rev.Cap += df;
            ret += df; f -= df;
            if (f == 0) break;
        }
        return ret;

    }
    class Edge
    {
        public static void Link(Edge e1, Edge e2)
        {
            e1.Rev = e2; e2.Rev = e1;
        }
        public int To { get; private set; }
        public Edge Rev { get; private set; }
        public int Cap { get; set; }
        public Edge(int t, int c)
        {
            To = t;
            Cap = c;
        }
        public override string ToString()
        {
            return string.Format("to: {0}, cap: {1}", To, Cap);
        }
    }
}
#region Template
public class Template
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmin<T>(ref T num, T val) where T : IComparable<T>
    { if (num.CompareTo(val) == 1) { num = val; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static bool chmax<T>(ref T num, T val) where T : IComparable<T>
    { if (num.CompareTo(val) == -1) { num = val; return true; } return false; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void swap<T>(ref T v1, ref T v2)
    { var t = v2; v2 = v1; v1 = t; }
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T[] Create<T>(int n, Func<T> f)
        => Enumerable.Repeat(0, n).Select(_ => f()).ToArray();
    public static void Fail() => Fail("No");
    public static void Fail<T>(T s) { Console.WriteLine(s); Console.Out.Close(); Environment.Exit(0); }
    static void Main(string[] args)
    {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        var p = new Solver();
        for (var i = 1; i > 0; --i)
            p.Solve();
        Console.Out.Flush();
    }
}

public class Input
{
    public static string read => Console.ReadLine().Trim();
    public static int[] ar => read.Split(' ').Select(int.Parse).ToArray();
    public static int num => Convert.ToInt32(read);
    public static long[] arL => read.Split(' ').Select(long.Parse).ToArray();
    public static long numL => Convert.ToInt64(read);
    public static char[][] grid(int h)
        => Create(h, () => read.ToCharArray());
    public static int[] ar1D(int n)
        => Create(n, () => num);
    public static long[] arL1D(int n)
        => Create(n, () => numL);
    public static string[] strs(int n)
        => Create(n, () => read);
    public static int[][] ar2D(int n)
        => Create(n, () => ar);
    public static long[][] arL2D(int n)
        => Create(n, () => arL);
    public static List<T>[] edge<T>(int n)
        => Create(n, () => new List<T>());
    public static void Make<T1, T2>(out T1 v1, out T2 v2)
    {
        v1 = Next<T1>();
        v2 = Next<T2>();
    }
    public static void Make<T1, T2, T3>(out T1 v1, out T2 v2, out T3 v3)
    {
        Make(out v1, out v2);
        v3 = Next<T3>();
    }
    public static void Make<T1, T2, T3, T4>(out T1 v1, out T2 v2, out T3 v3, out T4 v4)
    {
        Make(out v1, out v2, out v3);
        v4 = Next<T4>();
    }
    public static void Make<T1, T2, T3, T4, T5>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5)
    {
        Make(out v1, out v2, out v3, out v4);
        v5 = Next<T5>();
    }
    public static void Make<T1, T2, T3, T4, T5, T6>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6)
    {
        Make(out v1, out v2, out v3, out v4, out v5);
        v6 = Next<T6>();
    }
    static Input()
    {
        sc = new Queue<string>();
        dic = new Dictionary<Type, Func<string, object>>();
        dic[typeof(int)] = s => int.Parse(s);
        dic[typeof(long)] = s => long.Parse(s);
        dic[typeof(char)] = s => char.Parse(s);
        dic[typeof(double)] = s => double.Parse(s);
        dic[typeof(uint)] = s => uint.Parse(s);
        dic[typeof(ulong)] = s => ulong.Parse(s);
        dic[typeof(string)] = s => s;
    }
    private static Dictionary<Type, Func<string, object>> dic;
    private static Queue<string> sc;
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static T Next<T>() { if (sc.Count == 0) foreach (var item in read.Split(' ')) sc.Enqueue(item); return (T)dic[typeof(T)](sc.Dequeue()); }
    public const int MOD = 1000000007;
}

public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1;
    public T2 v2;
    public Pair() { v1 = default(T1);v2 = default(T2); }
    public Pair(T1 v1, T2 v2)
    { this.v1 = v1; this.v2 = v2; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public override string ToString()
        => $"{v1.ToString()} {v2.ToString()}";
}

public class Pair<T1, T2, T3> : Pair<T1, T2>, IComparable<Pair<T1, T2, T3>>
{
    public T3 v3;
    public Pair() : base() { v3 = default(T3); }
    public Pair(T1 v1, T2 v2, T3 v3) : base(v1, v2)
    { this.v3 = v3; }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public int CompareTo(Pair<T1, T2, T3> p)
    {
        var c = base.CompareTo(p);
        if (c == 0)
            c = Comparer<T3>.Default.Compare(v3, p.v3);
        return c;
    }
    public override string ToString()
        => $"{base.ToString()} {v3.ToString()}";
}
#endregion


Measured memory_bytes: 13908