//#define ACM_LOCAL 1
#if 1

#include<bits/stdc++.h>

#ifdef ONLINE_JUDGE
#define endl '\n'
#endif
using namespace std;
typedef long long ll;
const ll mod(998244353);
const ll MAXN(2e7 + 7);
const double eps(1e-6);

inline ll powmod(ll a, ll b) {
    ll res = 1;
    a %= mod;
    assert(b >= 0);
    for (; b; b >>= 1) {
        if (b & 1)res = res * a % mod;
        a = a * a % mod;
    }
    return res % mod;
}

inline ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }

struct GlobalData {
    string s, t;
    int ans;

public:
    void init() {
        ans = 0;
    }

    void input() {
        cin >> s >> t;
    }

    void outputAns() {
        cout << ans << endl;
    }

    void preSolve() {}
} globalData;

inline void preSolve() {
    globalData.preSolve();
}

inline void input() {
    globalData.init();
    globalData.input();
}

inline void output() {
    globalData.outputAns();
}

inline void addMod(int &a, const int &b) {
    a = (1ll*a+b)%mod;
}

inline void solve() {

    int n = globalData.s.size(), m = globalData.t.size();
    vector<vector<vector<int>>> dp(n+1, vector<vector<int>>(m+1, vector<int>(3)));
    dp[0][0][2] = 1;
    for(int i=0; i<=n; i++) {
        for(int j=0; j<=m; j++) {
            dp[i][j][2] = 1;    // 无前缀情况
            // dp[i+1][j][0] = dp[i][j][0] + dp[i][j][1] + dp[i][j][2]
            if(i<n) {
                if (j > 0 && globalData.s[i] != globalData.t[j - 1]) addMod(dp[i + 1][j][0], dp[i][j][1]);
                if (i > 0 && globalData.s[i] != globalData.s[i - 1]) addMod(dp[i + 1][j][0], dp[i][j][0]);
                addMod(dp[i + 1][j][0], dp[i][j][2]);
            }
            if(j<m) {
                if (j > 0 && globalData.t[j] != globalData.t[j - 1]) addMod(dp[i][j + 1][1], dp[i][j][1]);
                if (i > 0 && globalData.t[j] != globalData.s[i - 1]) addMod(dp[i][j + 1][1], dp[i][j][0]);
                addMod(dp[i][j + 1][1], dp[i][j][2]);
            }
        }
    }
    for(int i=1; i<=n; i++) for(int j=1; j<=m; j++) for(int k=0; k<2; k++) addMod(globalData.ans, dp[i][j][k]);
    int val = 0;
    for(int i=0; i<n; i++) {
        if(i>0 && globalData.s[i]!=globalData.s[i-1]) val += m;
        else val = m;
        globalData.ans -= val;
    }
    for(int j=0; j<m; j++) {
        if(j>0 && globalData.t[j]!=globalData.t[j-1]) val += n;
        else val = n;
        globalData.ans -= val;
    }
    globalData.ans = (1ll * globalData.ans + mod)%mod;

}

int main() {

#ifdef ACM_LOCAL
    freopen("./data/9.in", "r", stdin);
    freopen("./data/9.out", "w", stdout);
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    preSolve();
    int T = 1;
//    cin >> T;
    while (T--) {
        input();
        solve();
        output();
    }

    return 0;

}

#endif