#include<cstdio>
#include<vector>
#include<queue>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<ctime>
#include<random>
#include<assert.h>
#define pb emplace_back
#define mp make_pair
#define fi first
#define se second
#define dbg(x) cerr<<"In Line "<< __LINE__<<" the "<<#x<<" = "<<x<<'\n';
#define dpi(x,y) cerr<<"In Line "<<__LINE__<<" the "<<#x<<" = "<<x<<" ; "<<"the "<<#y<<" = "<<y<<'\n';
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int>pii;
typedef pair<ll,int>pli;
typedef pair<ll,ll>pll;
typedef pair<int,ll>pil;
typedef vector<int>vi;
typedef vector<ll>vll;
typedef vector<pii>vpii;
typedef vector<pil>vpil;
template<typename T>T cmax(T &x, T y){return x=x>y?x:y;}
template<typename T>T cmin(T &x, T y){return x=x<y?x:y;}
template<typename T>
T &read(T &r){
	r=0;bool w=0;char ch=getchar();
	while(ch<'0'||ch>'9')w=ch=='-'?1:0,ch=getchar();
	while(ch>='0'&&ch<='9')r=r*10+(ch^48),ch=getchar();
	return r=w?-r:r;
}
template<typename T1,typename... T2>
void read(T1 &x,T2& ...y){read(x);read(y...);}
const int mod=998244353;
inline void cadd(int &x,int y){x=(x+y>=mod)?(x+y-mod):(x+y);}
inline void cdel(int &x,int y){x=(x-y<0)?(x-y+mod):(x-y);}
inline int add(int x,int y){return (x+y>=mod)?(x+y-mod):(x+y);}
inline int del(int x,int y){return (x-y<0)?(x-y+mod):(x-y);}
int qpow(int x,int y){
	int s=1;
	while(y){
		if(y&1)s=1ll*s*x%mod;
		x=1ll*x*x%mod;
		y>>=1;
	}
	return s;
}
namespace MyPoly
{
	const int T=18;//2^T>n+m
	int inv[(1<<T)+10],fac[(1<<T)+10];
	int w[T][(1<<(T-1))+10],iw[T][(1<<(T-1))+10];
	void prework(){
		fac[0]=1;
		for(int i=1;i<=(1<<T);i++)fac[i]=1ll*fac[i-1]*i%mod;
		inv[1<<T]=qpow(fac[1<<T],mod-2);
		for(int i=(1<<T)-1;~i;--i)inv[i]=1ll*inv[i+1]*(i+1)%mod;
		for(int i=0;i<T;i++){
			int n=1<<(i+1);
			int W=qpow(3,(mod-1)/n);
			int IW=qpow(332748118,(mod-1)/n);
			w[i][0]=1;
			iw[i][0]=1;
			for(int j=1;j<n/2;j++)w[i][j]=1ll*w[i][j-1]*W%mod,iw[i][j]=1ll*iw[i][j-1]*IW%mod;
		}
	}
	struct Poly{
		vi a;
		Poly(){vi().swap(a);}
		Poly(int n){vi().swap(a);a.resize(n);}
		int size(){return a.size();}
		void resize(int x){a.resize(x);}
		int &operator[](int i){return a[i];}
		void print(){for(auto i:a)cout<<i<<' ';puts("");}
	};
	void DFT(Poly &a){ //转置
		int n=a.size();
		int p=__builtin_ctz(n);
		for(int i=n/2;i;i>>=1){
			--p;
			for(int j=0;j<n;j+=i<<1){
				for(int k=0;k<i;++k){
					int u=a[j+k],v=a[j+i+k];
					a[j+k]=add(u,v);
					a[j+i+k]=del(1ll*u*w[p][k]%mod,1ll*v*w[p][k]%mod);
				}
			}
		}
	}
	void IDFT(Poly &a){
		int n=a.size();
		int p=-1;
		for(int i=1;i<n;i<<=1){
			++p;
			for(int j=0;j<n;j+=i<<1){
				for(int k=0;k<i;++k){
					int v=1ll*a[j+i+k]*iw[p][k]%mod;
					a[j+i+k]=del(a[j+k],v);
					cadd(a[j+k],v);
				}
			}
		}
		int iv=qpow(n,mod-2);
		for(int i=0;i<n;i++)
			a[i]=1ll*a[i]*iv%mod;
	}
	Poly operator-(Poly f,Poly g){
		int n=max(f.size(),g.size());
		f.resize(n);g.resize(n);
		for(int i=0;i<n;i++)cdel(f[i],g[i]);
		return f;
	}
	Poly operator*(Poly f,Poly g){
		int n=f.size(),m=g.size();
		if (1ll*n*m<=1000){
			Poly h;
			h.resize(n+m-1);
			for(int i=0;i<n;i++)
				if(f[i])
					for(int j=0;j<m;j++)
						if(g[j])
							cadd(h[i+j],1ll*f[i]*g[j]%mod);
			return h;
		}
		int len=1,ct=0;
		while(len<=n+m)len<<=1,++ct;
		f.resize(len);
		g.resize(len);
		DFT(f);
		DFT(g);
		for(int i=0;i<len;i++)
			f[i]=1ll*f[i]*g[i]%mod;
		IDFT(f);
		f.resize(n+m-1);
		return f;
	}
}
using namespace MyPoly;
int bostan_mori(Poly &p,Poly &q,ll n){
	//[x^n]p(x)/q(x)
	auto adjust=[&](Poly &f,int o){
		int i;
		for(i=o;i<(int)f.size();i+=2)
			f[i/2]=f[i];
		f.resize(i/2);
	};
	while(n){
		int o=(n&1);n>>=1;
		Poly rq=q;
		for(int i=1;i<(int)rq.size();i+=2)rq[i]=del(0,rq[i]);
		q=q*rq;
		adjust(q,0);
		p=p*rq;
		if(!o)adjust(p,0);
		else adjust(p,1);
	}
	if(p.size())return 1ll*p[0]*qpow(q[0],mod-2)%mod;
	return 0;
}
int n,m;
int nxt[100010];
char s[100010];
signed main(){
	#ifdef do_while_true
//		assert(freopen("data.in","r",stdin));
//		assert(freopen("data.out","w",stdout));
	#endif
	prework();
	read(n,m);
	scanf("%s",s+1);
	for(int i=2,j=0;i<=n;i++){
		while(j&&s[j+1]!=s[i])j=nxt[j];
		if(s[j+1]==s[i])++j;
		nxt[i]=j; 
	}
	int x=nxt[n];
	Poly P(n+1),Q(n);
	P[n]=mod-1;
	while(x)Q[n-x]=1,x=nxt[x];
	Q[0]=1;
	Poly G(2);G[0]=1,G[1]=mod-26;
	Q=Q*G;
	P=Q-P;
	int ans=bostan_mori(Q,P,m);
	cout<<del(0,ans)<<'\n';
    #ifdef do_while_true
//		cerr<<'\n'<<"Time:"<<1.0*clock()/CLOCKS_PER_SEC*1000<<" ms"<<'\n';
	#endif
	return 0;
}