#include <bits/stdc++.h>
using namespace std;
const int MAX = 2005;
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
char dir[4] = {'>', '<', 'v', '^'};
char a[MAX][MAX];
int dis[MAX][MAX];
void bfs(queue<pair<int, int> > &q, bool mark[MAX][MAX], bool update) {
  while (!q.empty()) {
    pair<int, int> f = q.front();
    mark[f.first][f.second] = true;
    q.pop();
    for (int i = 0; i < 4; i++) {
      int x = f.second + dx[i];
      int y = f.first + dy[i];
      if (a[y][x] == dir[i]) {
        if (update) dis[y][x] = dis[f.first][f.second] + 1;
        q.push(make_pair(y, x));
      }
    }
  }
}
struct Node {
  int i, j;
  Node(int i_in, int j_in) {
    i = i_in;
    j = j_in;
  }
  bool operator<(const Node a) const { return (dis[i][j] < dis[a.i][a.j]); }
};
pair<int, int> go(pair<int, int> p) {
  int i = p.first;
  int j = p.second;
  if (a[i][j] == '^')
    i--;
  else if (a[i][j] == 'v')
    i++;
  else if (a[i][j] == '<')
    j--;
  else
    j++;
  return make_pair(i, j);
}
pair<int, int> path(pair<int, int> p) {
  int i = go(p).first;
  int j = go(p).second;
  if (a[i][j] == '#') return p;
  return path(go(p));
}
queue<pair<int, int> > q;
bool mark1[MAX][MAX], mark2[MAX][MAX];
vector<Node> vec;
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) cin >> a[i][j];
  int arrow = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
      if (a[i][j] != '#') {
        arrow++;
        int y = go(make_pair(i, j)).first;
        int x = go(make_pair(i, j)).second;
        if (a[y][x] == '#') {
          q.push(make_pair(i, j));
          dis[i][j] = 1;
        }
      }
  if (arrow == 0) {
    cout << 0 << endl;
    return 0;
  }
  bfs(q, mark1, true);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
      if (a[i][j] != '#' && !mark1[i][j]) {
        cout << -1 << endl;
        return 0;
      } else if (a[i][j] != '#')
        vec.push_back(Node(i, j));
  sort(vec.begin(), vec.end());
  Node last = vec[vec.size() - 1];
  q.push(path(make_pair(last.i, last.j)));
  bfs(q, mark2, false);
  for (int i = vec.size() - 2; i >= 0; i--) {
    int lastDis = dis[last.i][last.j];
    int nowDis = dis[vec[i].i][vec[i].j];
    if (lastDis != nowDis || !mark2[vec[i].i][vec[i].j]) {
      cout << lastDis + nowDis << endl;
      return 0;
    }
  }
  cout << 1 << endl;
}
