E

#include <bits/stdc++.h>

using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)
#define pb     push_back
#define ff     first
#define ss     second

int main()
{
    int n, m;
    cin>>n>>m;

    vector<string> s(n);
    for(auto &e: s)   cin>>e;

    int sx, sy;
    int ex, ey;

    vector<vector<int>> blocked(n, vector<int> (n, 0));

    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            if(s[i][j] == 'S')
            {
                sx = i;
                sy = j;
            }

            if(s[i][j] == 'G')
            {
                ex = i;
                ey = j;
                s[i][j] = '.';
            }

            if(s[i][j] == '<')
            {
                for(int k=j-1; k>=0; k--)
                {
                    if(s[i][k] != '.')      break;
                    blocked[i][k] = 1;
                }
            }

            if(s[i][j] == '>')
            {
                for(int k=j+1; k<n; k++)
                {
                    if(s[i][k] != '.')      break;
                    blocked[i][k] = 1;
                }
            }

            if(s[i][j] == '^')
            {
                for(int k=i-1; k>=0; k--)
                {
                    if(s[k][j] != '.')      break;
                    blocked[k][j] = 1;
                }
            }

            if(s[i][j] == 'v')
            {
                for(int k=i+1; k<n; k++)
                {
                    if(s[k][j] != '.')      break;
                    blocked[k][j] = 1;
                }
            }
        }
    }

    vector<vector<int>> vis(n, vector<int> (n, 0));
    vis[sx][sy] = 1;

    queue<pair<int, int>> qp;
    qp.push({sx, sy});

    while(qp.size())
    {
        auto e = qp.front();
        qp.pop();

        int i = e.ff;
        int j = e.ss;
        int c = vis[i][j];

        if(i-1>=0 && !vis[i-1][j] && s[i-1][j]=='.' && !blocked[i-1][j])
            vis[i-1][j]=c+1, qp.push({i-1, j});
        if(i+1<n && !vis[i+1][j] && s[i+1][j]=='.' && !blocked[i+1][j])
            vis[i+1][j]=c+1, qp.push({i+1, j});
        if(j-1>=0 && !vis[i][j-1] && s[i][j-1]=='.' && !blocked[i][j-1])
            vis[i][j-1]=c+1, qp.push({i, j-1});
        if(j+1<n && !vis[i][j+1] && s[i][j+1]=='.' && !blocked[i][j+1])
            vis[i][j+1]=c+1, qp.push({i, j+1});
    }

    cout<<vis[ex][ey] - 1<<"\n";
}