#include <bits/stdc++.h>
using namespace std;
char s[2010][2010];
int vis[2010][2010];
int to[2010][2010];
int val[2010][2010];
int solve(int i, int j, int c) {
  if (s[i][j] == '#') {
    return 0;
  }
  vis[i][j] = c;
  int ti = i, tj = j;
  if (s[i][j] == '>')
    tj++;
  else if (s[i][j] == '<')
    tj--;
  else if (s[i][j] == '^')
    ti--;
  else
    ti++;
  if (vis[ti][tj]) {
    if (vis[ti][tj] == c) {
      val[i][j] = -1;
    } else if (val[ti][tj] == -1) {
      val[i][j] = -1;
    } else {
      val[i][j] = val[ti][tj] + 1;
    }
  } else {
    int tmp = solve(ti, tj, c);
    if (tmp == -1)
      val[i][j] = -1;
    else
      val[i][j] = tmp + 1;
  }
  if (val[i][j] == 1)
    to[i][j] = i * 2010 + j;
  else
    to[i][j] = to[ti][tj];
  return val[i][j];
}
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) {
    scanf("%s", s[i]);
  }
  int c = 0, mx = 0, cur = 0, diff = 1;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (!vis[i][j]) {
        solve(i, j, ++c);
      }
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (val[i][j] == -1)
        mx = -1;
      else if (mx >= 0 && val[i][j] > mx) {
        mx = val[i][j];
        cur = to[i][j];
      }
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (val[i][j] == mx && to[i][j] != cur) diff = 0;
    }
  }
  if (mx == 0 || mx == -1)
    printf("%d\n", mx);
  else
    printf("%d\n", mx * 2 - diff);
  return 0;
}
