#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
struct DSU {
vector<vector<array<int, 2>>> par;
vector<vector<int>> sz;
void init (int N, int M) {
par.resize(N + 1);
sz.resize(N + 1);
for (int i = 0;i < N;i ++) {
par[i].assign(M + 1, {-1, -1});
sz[i].assign(M + 1, 1);
}
}
array<int, 2> get_par (array<int, 2> x) {
if (par[x[0]][x[1]][0] == -1) return x;
return par[x[0]][x[1]] = get_par(par[x[0]][x[1]]);
}
void add (array<int, 2> a, array<int, 2> b) {
a = get_par(a);
b = get_par(b);
if (a == b) return;
if (sz[a[0]][a[1]] < sz[b[0]][b[1]]) swap (a, b);
sz[a[0]][a[1]] += sz[b[0]][b[1]];
par[b[0]][b[1]] = a;
}
};
int32_t main () {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int N, M;
cin >> N >> M;
vector<vector<int>> arr(N, vector<int>(M));
map<char, int> val;
val['.'] = 1;
val['F'] = 2;
val['R'] = 3;
for (int i = 0;i < N;i ++) {
string S;
cin >> S;
for (int j = 0;j < M;j ++) {
arr[i][j] = val[S[j]];
}
}
assert (arr[0][0] == arr[N - 1][M - 1] && arr[0][0] > 1);
// for (int i = 0;i < N;i ++) {
// for (int j = 0;j < M;j ++) {
// cout << arr[i][j] << " ";
// } cout << "\n";
// } cout << "\n";
DSU DS;
DS.init (N, M);
vector<int> X = {1, -1, 0, 0};
vector<int> Y = {0, 0, 1, -1};
vector<vector<int>> used(N, vector<int>(M, 0)), submx(N, vector<int>(M, 0));
map<array<int, 2>, set<array<int, 2>>> g;
auto check = [&](int x, int y) -> bool {
if (x < 0 || x >= N || y < 0 || y >= M || used[x][y] == 1 || arr[x][y] <= 1) return 0;
return 1;
};
for (int i = 0;i < N;i ++) {
for (int j = 0;j < M;j ++) {
for (int t = 0;t < 4;t ++) if (check (i + X[t], j + Y[t])) {
if (arr[i][j] == arr[i + X[t]][j + Y[t]]) {
DS.add ({i, j}, {i + X[t], j + Y[t]});
}
}
}
}
for (int i = 0;i < N;i ++) for (int j = 0;j < M;j ++) used[i][j] = 0;
function<void(int, int)> dfss = [&](int sx, int sy) -> void {
used[sx][sy] = 1;
for (int i = 0;i < 4;i ++) if (check (X[i] + sx, Y[i] + sy) == true) {
if (arr[sx][sy] == arr[X[i] + sx][Y[i] + sy]) {
dfss (X[i] + sx, Y[i] + sy);
} else {
if (DS.get_par ({sx, sy}) != DS.get_par ({X[i] + sx, Y[i] + sy})) {
if (g[DS.get_par ({sx, sy})].find(DS.get_par ({X[i] + sx, Y[i] + sy})) == g[DS.get_par ({sx, sy})].end() && g[DS.get_par ({X[i] + sx, Y[i] + sy})].find(DS.get_par ({sx, sy})) == g[DS.get_par ({sx + X[i], sy + Y[i]})].end()) {
g[DS.get_par ({sx, sy})].insert(DS.get_par ({X[i] + sx, Y[i] + sy}));
}
}
dfss (X[i] + sx, Y[i] + sy);
}
}
};
dfss (0, 0);
// queue<array<int, 4>> q;
// q.push({0, 0, 0, 0});
// used[0][0] = 1;
// while (q.size() > 0) {
// auto [sx, sy, _x, _y] = q.front();
// q.pop();
// for (int i = 0;i < 4;i ++) if (check (X[i] + sx, Y[i] + sy) == true) {
// if (arr[sx][sy] != arr[X[i] + sx][Y[i] + sy]) {
// used[X[i] + sx][Y[i] + sy] = 1;
// g[{_x, _y}].push_back({X[i] + sx, Y[i] + sy});
// q.push({X[i] + sx, Y[i] + sy, X[i] + sx, Y[i] + sy});
// // dfs_init (X[i] + sx, Y[i] + sy, X[i] + sx, Y[i] + sy);
// } else {
// }
// }
// }
function<void(int, int)> dfs = [&](int sx, int sy) -> void {
// cout << sx << " " << sy << " -- ";
// for (auto [vx, vy] : g[{sx, sy}]) {
// cout << vx << " " << vy << ", ";
// } cout << "\n";
for (auto [vx, vy] : g[{sx, sy}]) {
dfs (vx, vy);
submx[sx][sy] = max(submx[sx][sy], submx[vx][vy]);
}
submx[sx][sy] ++;
};
dfs (0, 0);
cout << submx[0][0] << "\n";
}
/*
5 6
RRRRRR
.R...R
FRRFRR
FR....
.RRRRR
*/
