#include <bits/stdc++.h>

using namespace std;

const int inf = 0x3f3f3f3f;

const double eps = 1e-6;

const int N = 3e5+7;

typedef long long ll;

const ll mod = 998244353 ;

using namespace std;

vector<int> G[N];

int d[N],vis[N];

ll qpow(ll a,ll b){

    ll ans=1; ll base=a;

    while(b){

        if(b&1) ans=ans*base%mod;

        base=base*base%mod;

        b>>=1;

    }

    return ans;

}

ll res=1;

ll num=0;

void dfs(int u,int fa,int cnt){

    //cout<<u<<endl;

    d[u]=cnt;

    for(int i=0;i<G[u].size();i++){

        int v=G[u][i];

        if(v==fa) continue;

        if(!vis[v]){

            vis[v]=1;

            dfs(v,u,cnt+1);

            vis[v]=2;

        }else if(vis[v]==1){

            //cout<<cnt-d[v]+1<<endl;

            res=res*(qpow(2,cnt-d[v]+1)-1)%mod;

            num+=(cnt-d[v]+1);

        }else if(vis[v]==2){

        }

    }

}

int main(){

    ios::sync_with_stdio(false);

    cin.tie(0); cout.tie(0);

    int n,m;

    while(cin>>n>>m){

        for(int i=1;i<=n;i++) G[i].clear();

        memset(vis,0,sizeof(vis));

        memset(d,0,sizeof(d));

        res=1;

        num=0;

        for(int i=1;i<=m;i++){

            int u,v; cin>>u>>v;

            G[u].push_back(v);

            G[v].push_back(u);

        }

        vis[1]=1;

        dfs(1,0,1);

    //    for(int i=1;i<=n;i++)

    //        cout<<d[i]<<endl;

    //    cout<<res<<endl;

        //cout<<num<<endl;

        cout<<res*qpow(2,m-num)%mod<<endl;

    }

    return 0;

}

#include <bits/stdc++.h>

using namespace std;

const int inf = 0x3f3f3f3f;

const double eps = 1e-6;

const int N = 1e7+7 ;

typedef long long ll;

const ll mod = 998244353 ;

using namespace std;

int nextt[N];

void get_next(string s){

    nextt[1]=0;

    int len=s.length();

    for(int i=2,j=0;i<=len;i++){

        while(j>0&&s[j]!=s[i-1]) j=nextt[j];

        if(s[j]==s[i-1]) j++;

        nextt[i]=j;

    }

}

int main(){

    ios::sync_with_stdio(false);

    cin.tie(0); cout.tie(0);

    ll a,b;

    while(cin>>a>>b){

        string s; cin>>s;

        int len=s.length();

        int po=0;

        for(int i=0;i<len;i++){

            if(s[i]=='.'){

                po=i;

                break;

            }

        }

        s=s.substr(po+1,len-po-1);

        reverse(s.begin(),s.end());

        get_next(s);

        len=s.length();

        ll ans=-inf;

        for(int i=1;i<=len;i++){

            ans=max(ans,a*i-b*(i-nextt[i]));

        }

        cout<<ans<<endl;

    }

    return 0;

}