#include <iostream>
#include <vector>

using namespace std;

constexpr int DX[] = {0, 1, 0, -1};
constexpr int DY[] = {1, 0, -1, 0};

int longest_path(const vector<vector<int> > &grid, int x = -1, int y = -1, int depth = 0) {
    const unsigned int r = grid.size(), c = grid[0].size();
    if (x == -1 && y == -1) {
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < c; j++) {
                if (grid[i][j] == r * c) {
                    x = i, y = j, depth = 1;
                    break;
                }
            }
        }
    }

    for (int i = 0; i < 4; i++) {
        int nx = x + DX[i], ny = y + DY[i];
        if (nx >= 0 && nx < grid.size() && ny >= 0 && ny < grid[0].size()
            && grid[nx][ny] == grid[x][y] - 1) {
            return longest_path(grid, nx, ny, depth + 1);
        }
    }
    return depth;
}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int r, c;
    cin >> r >> c;

    vector<vector<int> > grid(r, vector<int>(c));
    for (int i = 0; i < r; i++) {
        for (int j = 0; j < c; j++) {
            cin >> grid[i][j];
        }
    }
    cout << longest_path(grid) << endl;

    return 0;
}