/*
ID: <REDACTED>
LANG: C++14
TASK: snail
*/

#include <bits/stdc++.h>

using namespace std;

typedef vector <int> vi;

#define f0r(i, a) for (int i = 0; i < a; i++)

template <class T> inline void setmax (T &x,T y) { x = max(x, y); }

const int MAX = 125;

int n, b;

int visit[MAX][MAX];
vi dr = {-1, 0, 1, 0};  // 0 is up, 1 is right, 2 is down, 3 is left
vi dc = {0, 1, 0, -1};

bool valid(int r, int c) {  // Checks whether or not the coordinate is in the board
    return r >= 0 && r < n && c >= 0 && c < n;
}

int dfs (int r, int c, int dir) {
    visit[r][c] = 1;

    int ans = 0;
    if (valid(r + dr[dir], c + dc[dir]) && visit[r + dr[dir]][c + dc[dir]] == 0)    // It is empty
        ans = dfs(r + dr[dir], c + dc[dir], dir);
    else if (valid(r + dr[dir], c + dc[dir]) && visit[r + dr[dir]][c + dc[dir]] == 1)   // We have visited it before (already part of our path)
        ans = 0;
    else {  // We reached border or barrier and must turn
        int left = (dir + 3) % 4;
        int right = (dir + 1) % 4;
        if (valid(r + dr[left], c + dc[left]) && visit[r + dr[left]][c + dc[left]] == 0)
            setmax(ans, dfs(r + dr[left], c + dc[left], left));
        if (valid(r + dr[right], c + dc[right]) && visit[r + dr[right]][c + dc[right]] == 0)
            setmax(ans, dfs(r + dr[right], c + dc[right], right));
    }

    visit[r][c] = 0;
    return ans + 1;
}

int main() {
    //freopen("snail.in", "r", stdin);
    //freopen("snail.out", "w", stdout);

    f0r (i, MAX) f0r (j, MAX)
        visit[i][j] = 0;

    scanf(" %d %d ", &n, &b);

    char c;
    int r;
    f0r (i, b) {
        scanf(" %c %d ", &c, &r);
        visit[r - 1][c - 'A'] = 2;
    }

    cout << max(dfs(0, 0, 1), dfs(0, 0, 2)) << endl;
}