#include <bits/stdc++.h>
using namespace std;
#define io_speed_up ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
template<typename T>void rd(T&x){int f=0,c;while(!isdigit(c=getchar()))f^=!(c^45);x=(c&15);while(isdigit(c=getchar()))x=x*10+(c&15);if(f)x=-x;} //读整型
template<typename T>void pt(T x,int c=10){if(x<0)putchar('-'),x=-x;if(x>9)pt(x/10,-1);putchar(x%10+48);if(c!=-1)putchar(c);}
template<typename T>void umax(T&x,const T&y){if(x<y)x=y;}
template<typename T>void umin(T&x,const T&y){if(x>y)x=y;}
#define for_seq(i,s) for(int i=0;i<(int)s.size();i++)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define per(i,a,b) for(int i=a;i>=b;i--)
#define for1(i,n) for(int i=1;i<=n;i++)
#define for0(i,n) for(int i=0;i<n;i++)
#define ms(a,b)  memset(a,b,sizeof a)
#define all(n) (n).begin(), (n).end()
#define sz(x) (int)x.size()
#define fi first
#define se second
using ll = long long;
using ld = long double;
using pii = pair<int,int>;
using pll = pair<long,long>;
const int inf = 0x3f3f3f3f;
const int maxn = 1e3+5;
const int mod = 998244353;

int dp[maxn][maxn][2];
void add(int &x,int y) {
	x += y;
	if(x>=mod) x -= mod;
}
char s[maxn],t[maxn];
int f[maxn],g[maxn];
int main()
{
	io_speed_up;
	cin>>(s+1)>>(t+1);
	int n = strlen(s+1), m = strlen(t+1);
	rep(i,1,n) f[i] = 1 + (s[i]!=s[i-1]?f[i-1]:0);
	rep(i,1,m) g[i] = 1 + (t[i]!=t[i-1]?g[i-1]:0);
	int ans = 0;
	rep(i,1,n) {
		rep(j,1,m) {
			int &x = dp[i][j][0], &y = dp[i][j][1];
			if(s[i]!=s[i-1]) {
				add(x, dp[i-1][j][0]);
			}
			if(s[i]!=t[j]) {
				add(x, dp[i-1][j][1]);
				add(x, g[j]);

				add(y, dp[i][j-1][0]);
				add(y, f[i]);
			}
			if(t[j]!=t[j-1]) {
				add(y, dp[i][j-1][1]);
			}
			add(ans, x);
			add(ans, y);
		}
	}
	cout<<ans<<"\n";
	return 0;
}