using System;
using System.Linq;
using System.Diagnostics;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using StringBuilder = System.Text.StringBuilder;
//using System.Numerics;
using Number = System.Int64;
namespace Program
{

    public class Solver
    {
        public void Solve()
        {
            var n = sc.Integer() + 2;
            var m = sc.Integer() + 2;
            var S = Enumerate(n, x => x == 0 || x == n - 1 ? Enumerable.Repeat('#', m).AsString() : "#" + sc.Scan() + "#");
            int[] dx = { -1, 0, 1, 0, -1, 0, 1, 0 };
            int[] dy = { 0, 1, 0, -1, 0, 1, 0, -1 };
            int sx = -1, sy = -1, sd = -1;
            int gx = -1, gy = -1;
            string dir = "^>v<";
            var dist = new int[n, m, 4];
            for (int i = 0; i < n; i++)
            {
                Debug.WriteLine(S[i]);

                for (int j = 0; j < m; j++)
                {
                    if (S[i][j] == 'G') { gx = i; gy = j; }
                    for (int k = 0; k < 4; k++)
                    {
                        dist[i, j, k] = 1000000000;
                        if (S[i][j] == dir[k]) { sx = i; sy = j; sd = k; }
                    }
                }
            }

            dist[sx, sy, sd] = 0;
            var q = new Queue<int>();
            q.Enqueue(sx * 4 * m + sy * 4 + sd);
            var ok = false;
            while (q.Any())
            {
                var p = q.Dequeue();
                var x = p / (4 * m);
                var y = (p % (4 * m)) / 4;
                var d = p % 4;
                //Debug.WriteLine("{0} {1} {2}", x, y, dir[d]);
                //Debug.WriteLine(dist[x, y, d]);
                if (x == gx && y == gy)
                {
                    ok = true; break;
                }
                var nx = x + dx[d];
                var ny = y + dy[d];
                var nnx = nx + dx[d + 1];
                var nny = ny + dy[d + 1];
                if(S[nx][ny]=='G')//ゴールだったら進むんじゃ
                {
                    if (dist[nx, ny, d % 4] > dist[x, y, d])
                    {
                        dist[nx, ny, d % 4] = dist[x, y, d] + 1;
                        q.Enqueue((nx * 4 * m) + (ny * 4) + (d % 4));
                    }                    
                }
                else if (S[nx][ny] != '#' && S[nnx][nny] != '#')//交差点でぐるっとまわる
                {
                    if (dist[nnx, nny, (d + 1) % 4] > dist[x, y, d])
                    {
                        dist[nx, ny, d % 4] = dist[x, y, d] + 1;
                        dist[nnx, nny, (d + 1) % 4] = dist[x, y, d] + 2;
                        q.Enqueue((nnx * 4 * m) + (nny * 4) + ((d + 1) % 4));
                        Debug.WriteLine(dir[(d + 1) % 4]);

                    }
                }
                else if (S[nx][ny] != '#')//直進
                {
                    if (dist[nx, ny, d % 4] > dist[x, y, d])
                    {
                        dist[nx, ny, d % 4] = dist[x, y, d] + 1;
                        q.Enqueue((nx * 4 * m) + (ny * 4) + (d % 4));
                    }
                }
                else//壁沿いにまわる
                {
                    if (dist[x, y, (d + 3) % 4] > dist[x, y, d])
                    {
                        dist[x, y, (d + 3) % 4] = dist[x, y, d];
                        q.Enqueue((x * 4 * m) + (y * 4) + ((d + 3) % 4));
                    }
                }
            }
            if (!ok)
            {
                IO.Printer.Out.WriteLine(-1);
                return;
            }
            var cnt = 0;
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                {
                    for (int k = 0; k < 4; k++)
                    {
                        if (dist[i, j, k] < 1000000000) { cnt++; break; }
                    }
                }
            }
            IO.Printer.Out.WriteLine(cnt);




        }
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex
{
    static public string AsString(this IEnumerable<char> ie) { return new string(System.Linq.Enumerable.ToArray(ie)); }
    //static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") { return string.Join(st, ie); }
    static public void Main()
    {
        Debug.Listeners.Add(new TextWriterTraceListener(Program.IO.Printer.Out));
        var solver = new Program.Solver();
        solver.Solve();
        Program.IO.Printer.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer : StreamWriter
    {
        static Printer() { Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false }; }
        public static Printer Out { get; set; }
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(System.IO.Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
        public Printer(System.IO.Stream stream, Encoding encoding) : base(stream, encoding) { }
        public void Write<T>(string format, T[] source) { base.Write(format, source.OfType<object>().ToArray()); }
        public void WriteLine<T>(string format, T[] source) { base.WriteLine(format, source.OfType<object>().ToArray()); }
    }
    public class StreamScanner
    {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read()
        {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n'; b = (char)read())
                if (b == 0) break;
                else if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long()
        {
            if (isEof) return long.MinValue;
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != 0 && b != '-' && (b < '0' || '9' < b));
            if (b == 0) return long.MinValue;
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        public int Integer() { return (isEof) ? int.MinValue : (int)Long(); }
        public double Double() { var s = Scan(); return s != "" ? double.Parse(Scan(), CultureInfo.InvariantCulture) : double.NaN; }
        private T[] enumerate<T>(int n, Func<T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f();
            return a;
        }

        public char[] Char(int n) { return enumerate(n, Char); }
        public string[] Scan(int n) { return enumerate(n, Scan); }
        public double[] Double(int n) { return enumerate(n, Double); }
        public int[] Integer(int n) { return enumerate(n, Integer); }
        public long[] Long(int n) { return enumerate(n, Long); }
    }
}
#endregion


Measured memory_bytes: 14220