#include <iostream>
#include <algorithm>
#include <cstring>
constexpr int N(2010),p(998244353);
int fp(int a,int b){int ans(1),off(a);while(b){if(b&1) ans=1ll*ans*off%p;off=1ll*off*off%p;b>>=1;}return ans;}
int W(int k){return k>=p?k-p:k;}
int main()
{
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);static char s[N];
	int m;std::cin>>m>>(s+1);int n(std::strlen(s+1));
	static int v1[N],v2[N],fl[N];
	for(int i(2);i<=n;++i)
	{
		int j(fl[i-1]);while(j && s[j+1]!=s[i]) j=fl[j];
		if(s[j+1]==s[i]) ++j;fl[i]=j;
	}
	for(int i(0);i<=n;++i)
	{
		int mx(-1),mp(0),v(i==n?fl[i]:i);
		while(true)
		{
			if(s[v+1]-'a'+1>mx)
			{
				mx=s[v+1]-'a'+1;
				mp=v+1;
			}
			if(!v) break;
			v=fl[v];
		}
		// std::cerr<<i<<" "<<mx<<" "<<mp<<std::endl;
		v2[i]=mp;v1[i]=26-mx;
	}
	int ans(0);
	for(int i(1);i<=n;++i)
	{
		int u(i);
		for(int j(1);j<=m && u;++j) u=v2[u];
		if(u && u==i) ++ans;
	}
	static int f[N][N][2];f[0][0][0]=1;
	for(int i(0);i<m;++i)
	{
		for(int j(0);j<=n;++j)
		{
			f[i+1][0][1]=(f[i+1][0][1]+1ll*f[i][j][1]*v1[j]+1ll*f[i][j][0]*v1[j]*(i+1))%p;
			f[i+1][v2[j]][1]=W(f[i+1][v2[j]][1]+f[i][j][1]);
			f[i+1][v2[j]][0]=W(f[i+1][v2[j]][0]+f[i][j][0]);
		}
	}
	std::cout<<W(fp(26,m)-W(ans+f[m][0][1])+p)<<std::endl;
	return 0;
}