#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>
#include <ciso646>
#include <cassert>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef vector<ll> vec;

inline bool check(ll x, ll y, ll xMax, ll yMax) { return x >= 0 && y >= 0 && xMax > x && yMax > y; }
inline int toint(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string tostring(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }
template<class T> inline T mypow(T x, ll n) { T res = 1; while (n > 0) { if (n & 1)res = res * x;	x = x * x;	n >>= 1; }return res; }
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

#define For(i,a,b)	for(ll (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define rFor(i,a,b)	for(ll (i) = (a-1);i >= (b);(i)--)
#define rrep(i,n)	rFor(i,n,0)
#define each(i,n)	for(auto &i : n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define sz(a)		(sizeof(a))
#define tostr(a)	tostring(a)
#define dump(val) 	cerr << #val " = " << val << endl;
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)

const ll dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, -1, 0, 1, -1, 1, -1, 1 };

const ll mod = 1e9 + 7;
const ll INF = 1e17 + 9;

#define int ll
#define double ld

void surround(vector<string> &vs, int &h, int &w, char c) {
	vector<string> vs2;
	vs2.push_back(string(w + 2, c));
	rep(i, h) {
		vs2.push_back(string());
		vs2[i + 1] = c + vs[i] + c;
	}
	vs2.push_back(string(w + 2, c));
	h += 2, w += 2;
	vs = vs2;
}

signed main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);

	int N, M;
	cin >> N >> M;
	vector<string> s(N);

	map<char, int> table = { 
		{'v', 0},
		{'<', 1},
		{'^', 2},
		{'>', 3},
	};
	int sx, sy, gx, gy;
	int dir;

	rep(x, N) {
		cin >> s[x];
	}
	surround(s, N, M, '#');
	rep(x, N){
		rep(y, M) {
			if (table.count(s[x][y])) {
				sx = x, sy = y;
				dir = table[s[x][y]];
			}
			if (s[x][y] == 'G') {
				gx = x, gy = y;
			}
			if (s[x][y] != '#') {
				s[x][y] = '.';
			}
		}
	}

	bool visited[55][55][4];
	clr(visited);
	visited[sx][sy][dir] = true;
	while (sx != gx || sy != gy) {
		int nx[4], ny[4];
		rep(i, 4) {
			int t = (dir + i) % 4;
			nx[i] = sx + dx[t], ny[i] = sy + dy[t];
		}
		if (s[nx[1]][ny[1]] == '.') {
			sx = nx[1]; sy = ny[1]; dir = (dir + 1) % 4;
		}else
		if (s[nx[0]][ny[0]] == '.') {
			sx = nx[0]; sy = ny[0]; dir = (dir + 0) % 4;
		}else
		if (s[nx[3]][ny[3]] == '.') {
			sx = nx[3]; sy = ny[3]; dir = (dir + 3) % 4;
		}else
		if (s[nx[2]][ny[2]] == '.') {
			sx = nx[2]; sy = ny[2]; dir = (dir + 2) % 4;
		}
		else {
			cout << -1 << endl;
			return 0;
		}
		if (visited[sx][sy][dir]) {
			cout << -1 << endl;
			return 0;
		}
		visited[sx][sy][dir] = true;
	}
	int ans = 0;
	rep(x, N)rep(y, M) {
		rep(i, 4) {
			if (visited[x][y][i]) {
				ans++;
				break;
			}
		}
	}
	cout << ans << endl;

	return 0;
}

Measured memory_bytes: 3260