#include <time.h>
#include <iomanip>
#include <iostream>
#include <map>
#include <algorithm>
#include <queue>
#include <set>
#include <vector>
#include <iomanip>
#include <bitset>
using namespace std;
long long kq = 0 , f[1005][1005][3] , mod = 998244353;
string x , y;
void trau(int sti , int ste , int i , int e , string s)
{
	if (s.size() > 1)
	{
		if (s[s.size() - 1] == s[s.size() - 2])
		{
			return;
		}
		if (i != sti && e != ste)
		{
			cout <<sti<<" "<<ste<<" "<<i<<" "<<e<<" "<<s<<'\n';
			kq++;
		}
	}
	if (i+1 < x.size())
	{
		s += x[i+1];
		trau(sti , ste , i + 1 , e , s);
		s.pop_back();
	}
	if (e+1 < y.size())
	{
		s += y[e+1];
		trau(sti , ste , i , e + 1 , s);
		s.pop_back();
	}
}
int tt()
{
	for (int i = 1 ; i < x.size() ; i++)
	{
		for (int e = 1 ; e < y.size() ; e++)
		{
			trau(i-1 , e-1 , i-1 , e-1 , "");
		}
	}
	return kq;
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	srand (time(NULL));
	int test = 1;
	cin >> x;
	cin >> y;
	int n = x.size();
	int m = y.size();
	x = '.' + x;
	y = '/' + y;
	//cout <<tt()<<'\n';
	f[1][0][0] = 1;
	f[0][1][1] = 1;
	long long res = 0;
	for (int i = 2 ; i <= n ; i++)
	{
		if (x[i] != x[i-1])
		{
			f[i][0][0] = f[i-1][0][0] + 1;;
		}
		else
		{
			f[i][0][0] = 1;
		}
	}
	for (int i = 2 ; i <= m ; i++)
	{
		if (y[i] != y[i-1])
		{
			f[0][i][1] = f[0][i-1][1] + 1;
		}
		else
		{
			f[0][i][1] = 1;
		}
	}
	for (int i = 1 ; i <= n ; i++)
	{
		for (int e = 1 ; e <= m ; e++)
		{
			if (x[i] != x[i-1])
			{
				f[i][e][0] += f[i-1][e][0];
			}
			if (x[i] != y[e])
			{
				f[i][e][0] += f[i-1][e][1];
			}
			if (y[e] != x[i])
			{
				f[i][e][1] += f[i][e-1][0];
			}
			if (y[e] != y[e-1])
			{
				f[i][e][1] += f[i][e-1][1];
			}
			if (e != 1 && x[i] != y[e])
			{
				f[i][e][1] += f[i][0][0];
			}
			if (i != 1 && x[i] != y[e])
			{
				f[i][e][0]+=f[0][e][1];
			}
			f[i][e][0] %= mod;
			f[i][e][1] %= mod;
			res += f[i][e][0];
			res += f[i][e][1];
			res %= mod;
		//	cout <<i<<" "<<e<<" "<<f[i][e][0]<<" "<<f[i][e][1]<<'\n';
		}
	}
	cout <<res<<'\n';
}


