https://codeforces.com/contest/1096/problem/B

题解：只要数前后相同个数，再看头尾是不是相同

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=210000;
const int MOD=998244353;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
char str[N];
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d",&n);
    scanf("%s",str);
    ll ans=0;
    int a=0;
    int b=0;
    for(int i=0;i<n;i++){
        if(str[i]==str[0]){
            a++;
        }else{
            break;
        }
    }
    for(int j=n-1;j>=0;j--){
        if(str[j]==str[n-1]){
            b++;
        }else{
            break;
        }
    }
    if(str[0]==str[n-1]){
        ans=(1ll*(a+1)*(b+1))%MOD;
    }else{
        ans=(a+b+1)%MOD;
    }
    cout << ans << endl;
    //cout << "Hello world!" << endl;
    return 0;
}