#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define DUMP(x)  cerr << #x << " = " << (x) << endl;
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT_ON(bit, i) (bit & (1LL << i))

typedef long long LL;
template<typename T> using V = std::vector<T>;
template<typename T> using VV = std::vector<std::vector<T>>;
template<typename T> using VVV = std::vector<std::vector<std::vector<T>>>;
template<typename T> using VVVV = std::vector<std::vector<std::vector<std::vector<T>>>>;

template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline void print_vec(const std::vector<T> &v) { for (int i = 0; i < v.size(); ++i) {  if (i != 0) {std::cout << " ";} std::cout << v[i];} std::cout << "\n"; }
template<class T> inline bool inside(T y, T x, T H, T W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }
template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

const int INF = 1 << 30;
const double EPS = 1e-9;
const std::string YES = "YES", Yes = "Yes", NO = "NO", No = "No";
const std::vector<int> dy4 = { 0, 1, 0, -1 }, dx4 = { 1, 0, -1, 0 };    // 4近傍（右, 下, 左, 上）
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int M, N;
    cin >> M >> N;
    string S, T;
    cin >> S;
    cin >> T;

    V<int> s(M), t(N);
    FOR(i, 0, M) {
        s[i] = (S[i] == 'O');
    }
    FOR(i, 0, N) {
        t[i] = (T[i] == 'O');
    }


    // dp[i][j][k] = Sからi文字、Tからj文字みて最後がkのときの列車になれる最大
    VVV<int> dp(M + 1, VV<int>(N + 1, V<int>(2, 0)));


    FOR(i, 0, M) {
        if (s[i] == 0 or dp[i][0][0]) {
            chmax(dp[i + 1][0][s[i]], dp[i][0][!s[i]] + 1);
        }
    }
    FOR(j, 0, N) {
        if (t[j] == 0 or dp[0][j][0]) {
            chmax(dp[0][j + 1][t[j]], dp[0][j][!t[j]] + 1);
        }
    }

    int ans = 0;
    FOR(i, 0, M) {
        FOR(j, 0, N) {
            if (s[i] == 0 or dp[i][j + 1][0]) {
                chmax(dp[i + 1][j + 1][s[i]], dp[i][j + 1][!s[i]] + 1);
            }
            if (t[j] == 0 or dp[i + 1][j][0]) {
                chmax(dp[i + 1][j + 1][t[j]], dp[i + 1][j][!t[j]] + 1);
            }

            chmax(ans, dp[i + 1][j + 1][0]);
        }
    }

    print(ans);

    return 0;
}


Measured memory_bytes: 222072