#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

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

struct UnionFind {
	vector<int> v;
	UnionFind(int n) : v(n) { for (int i = 0; i < n; i++) v[i] = i; }
	int  find(int x) { return v[x] == x ? x : v[x] = find(v[x]); }
	void unite(int x, int y) { v[find(x)] = find(y); }
};

int main() {
	int h, w;
	cin >> h >> w;
	vector<string> cell(h);
	REP(i, h)
		cin >> cell[i];
	int gx, gy;
	int sx, sy, dir;
	REP(i, h) {
		REP(j, w) {
			if (cell[i][j] == 'G') {
				gy = i;
				gx = j;
			}
			if (cell[i][j] != 'G'&&cell[i][j] != '#'&&cell[i][j] != '.') {
				sy = i;
				sx = j;
				if (cell[i][j] == '<')
					dir = 0;
				if (cell[i][j] == 'v')
					dir = 1;
				if (cell[i][j] == '>')
					dir = 2;
				if (cell[i][j] == '^')
					dir = 3;
			}

		}
	}
	set<pii> visited;
	set<pair<pii, int>> G;
	bool clear = true;
	while (1) {
		visited.insert(pii(sy,sx));
		if (sx == gx&&sy == gy) {
			break;
		}
		if (G.find(pair<pii, int>(pii(sy, sx), dir)) != G.end()) {
			clear = false;
			break;
		}
		G.insert(pair<pii, int>(pii(sy, sx), dir));
		if (0 <= sx + dx[(dir + 3) % 4] && sx + dx[(dir + 3) % 4] < w && 0 <= sy + dy[(dir + 3) % 4] && sy + dy[(dir + 3) % 4] < h&&cell[sy + dy[(dir + 3) % 4]][sx + dx[(dir + 3) % 4]] != '#') {
			sx += dx[(dir + 3) % 4];
			sy += dy[(dir + 3) % 4];
			dir = (dir + 3) % 4;
			continue;
		}
		if (0 <= sx + dx[dir] && sx + dx[dir] < w && 0 <= sy + dy[dir] && sy + dy[dir] < h&&cell[sy + dy[dir]][sx + dx[dir]] != '#') {
			sx += dx[dir];
			sy += dy[dir];
			continue;
		}
		dir++;
		dir %= 4;
	}
	if (clear)
		cout << visited.size() << endl;
	else
		cout << -1 << endl;
}