#include <bits/stdc++.h>
using namespace std;
int n, m, status[2001][2001], g[4000001][5], kol[4000001], h;
char a[3000][3000];
bool f;
void dfs(int x, int y) {
  status[x][y] = 1;
  if (a[x][y] == '^') {
    if (status[x - 1][y] == 1)
      f = true;
    else if (status[x - 1][y] == 0)
      dfs(x - 1, y);
  }
  if (a[x][y] == '<') {
    if (status[x][y - 1] == 1)
      f = true;
    else if (status[x][y - 1] == 0)
      dfs(x, y - 1);
  }
  if (a[x][y] == '>') {
    if (status[x][y + 1] == 1)
      f = true;
    else if (status[x][y + 1] == 0)
      dfs(x, y + 1);
  }
  if (a[x][y] == 'v') {
    if (status[x + 1][y] == 1)
      f = true;
    else if (status[x + 1][y] == 0)
      dfs(x + 1, y);
  }
  status[x][y] = 2;
}
void dfs1(int v, int r) {
  h = max(h, r);
  for (size_t i = 1; i <= kol[v]; i++) dfs1(g[v][i], r + 1);
}
int main() {
  cin >> n >> m;
  scanf("\n");
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) cin >> a[i][j];
    scanf("\n");
  }
  f = false;
  memset(status, 0, sizeof(status));
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      if (!status[i][j]) dfs(i, j);
  if (f) {
    cout << -1;
    return 0;
  }
  memset(kol, 0, sizeof(kol));
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) {
      int v = (i - 1) * m + j, u;
      if (a[i][j] == '#') continue;
      if (a[i][j] == '^') u = (i - 2) * m + j;
      if (a[i][j] == '<') u = (i - 1) * m + j - 1;
      if (a[i][j] == '>') u = (i - 1) * m + j + 1;
      if (a[i][j] == 'v') u = i * m + j;
      kol[u]++;
      g[u][kol[u]] = v;
    }
  int mx1 = 0, mx2 = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) {
      if (a[i][j] == '#') {
        for (int ii = -1; ii <= 1; ii++)
          for (int jj = -1; jj <= 1; jj++)
            if (abs(ii + jj) == 1 && i + ii > 0 && i + ii <= n && j + jj > 0 &&
                j + jj <= m && a[i + ii][j + jj] != '#') {
              int x = i + ii, y = j + jj;
              if (a[i + ii][j + jj] == '^') x--;
              if (a[i + ii][j + jj] == 'v') x++;
              if (a[i + ii][j + jj] == '<') y--;
              if (a[i + ii][j + jj] == '>') y++;
              if (x != i || y != j) continue;
              int v = (i + ii - 1) * m + j + jj;
              h = 0;
              dfs1(v, 1);
              if (h >= mx1) {
                mx2 = mx1;
                mx1 = h;
              } else if (h > mx2)
                mx2 = h;
            }
      }
    }
  cout << max(2 * mx1 - 1, mx1 + mx2);
  return 0;
}
