#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define maxn 1000010
const int mod=1e9+7;
const int c=26;
char s[maxn];
int f[maxn];
int n,k;
ll pw(ll a,int n)
{
        ll res=1;
        while(n)
        {
                if(n&1)res=res*a%mod;
                a=a*a%mod,n>>=1;
        }
        return res;
}
ll INV(ll a){return pw(a,mod-2);}
void fail()
{
        f[0]=-1;
        for(int i=1;i<n;i++)
        {
                int j=f[i-1];
                while(j>=0 && s[j+1]!=s[i])j=f[j];
                if(s[j+1]==s[i])f[i]=j+1;
                else f[i]=j;
        }
}
int main()
{
        scanf("%d%d",&n,&k);
        scanf("%s",s);
        fail();
        //              for(int i=0;i<n;i++)printf("%d ",f[i]);puts("");
        //      printf("n = %d, k = %d\n",n,k);
        ll ans=0;
        int cur=n-1;
        while(cur!=-1)
        {
                if(2*n-(cur+1)>k)break;
                //              printf("cur = %d\n",cur);
                ans++,cur=f[cur];
        }
        if(k>=2*n)//1+c+...+c^m=(c^(m+1)-1)/(c-1)
        {
                int m=k-2*n;
                ll tmp=pw(c,m+1);
                tmp=(tmp-1+mod)%mod;
                tmp=tmp*INV(c-1)%mod;
                ans=(ans+tmp)%mod;
        }
        printf("%lld\n",ans);
        return 0;
}