/*
Hey  why peeping here -_'_- ?
I believe on myself and I will achieve
this->author = Fuad Ashraful Mehmet, CSE ,University of Asia Pacific
Todo:
https://www.youtube.com/watch?v=VoTUc-1qIT8&ab_channel=TipsJhankarGaane
https://codeforces.com/problemset/page/5?tags=1500-2500
*/
#include <bits/stdc++.h>
#define forn(i, n) for (int i = 0; i < (int)n; ++i)
#define all(o) (o).begin(), (o).end()
#define rall(o) (o).rbegin(), (o).rend()
#define sz(o) (o).size()
#define FAST_IO  ios_base::sync_with_stdio(0); cin.tie(nullptr); cout.tie(nullptr);
#define dbg(o) cerr << "at " << __LINE__ << " response = " << o << endl;
#define dbgA(a,L,R) cerr<<"A=[";for(int i=L;i<=R;i++) cerr<<a[i]<<(i==R?"]\n":" ");
#define dbgV(O) cerr << #O << "=["; for (auto o : O) cerr << o << ", "; cerr << "E]\n";
#define pb push_back
using namespace std;
using pii = pair<int, int>;
typedef long long ll;
int  n,m,k,tc=1,q,cs=1,lx,ly;
const int N=1005;

ll dp[N][N][3][2][2];
string x,y;
const ll mod=998244353;

void relax(ll &num)
{
	num%=mod;
	if(num<0)
	num+=mod;
	return;
}

ll go(int i,int j,int prev,bool f1,bool f2)
{
	//if(i>=lx or j>=ly) return 0;
	ll &ret=dp[i][j][prev][f1][f2];
	if(-1!=ret)
		return ret;
	
	if(prev==0)
		prev=x[i-1]-'a';
	else if(prev==1)
		prev=y[j-1]-'a';
	else prev=27;
	ret=f1&f2;
	if(i<lx)
	if(prev!=x[i]-'a')ret+=go(i+1,j,0,f1|1,f2);
	relax(ret);
	if(j<ly)
	if(prev!=y[j]-'a')ret+=go(i,j+1,1,f1,f2|1);
	relax(ret);

	return ret;
}
void Solve()
{
	memset(dp,-1,sizeof dp);
	cin>>x>>y;
	lx=sz(x);
	ly=sz(y);

	ll ans=0;
	forn(i,lx)
	{
		forn(j,ly)
		{
			ans+=go(i,j,2,0,0);
			relax(ans);
		}
	}

	cout<<ans<<'\n';
	return;
	
}

int main()
{
	FAST_IO
	//cout<<setprecision(20)<<fixed;
	//cin>>tc;
	while(tc--)
	{
		Solve();
	}
	return 0;
}