#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rof(i,a,b) for(int i=(a);i>=(b);--i)
using namespace std;
const int Maxn=1e6,Mod=998244353,i2=(Mod+1)/2;

inline int read()
{
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0' || ch>'9')
    {
        if(ch=='-') f=-1;
        ch=getchar();
    }
    while(ch>='0' && ch<='9')
    {
        x=x*10+ch-'0';
        ch=getchar();
    }
    return x*f;
}
inline int Pow(int x,int y)
{
    int res=1;
    while(y)
    {
        if(y&1) res=1ll*res*x%Mod;
        x=1ll*x*x%Mod,y>>=1;
    }
    return res;
}

int n,m,ans,a[Maxn+5],fac[Maxn+5],inv[Maxn+5],vis[Maxn+5];
inline int C(int x,int y) {return 1ll*fac[x]*inv[x-y]%Mod*inv[y]%Mod;}

int main()
{
    // freopen("1.in","r",stdin);

    n=read(),m=read(); fac[0]=inv[0]=1;
    For(i,1,Maxn) fac[i]=1ll*fac[i-1]*i%Mod;
    inv[Maxn]=Pow(fac[Maxn],Mod-2);
    Rof(i,Maxn-1,1) inv[i]=1ll*inv[i+1]*(i+1)%Mod;
    For(i,1,m) a[i]=read(),vis[a[i]]=1;
    int p=m; For(i,1,m-1) if(a[i]>a[i+1]) {p=i; break;}
    For(i,p+1,m) vis[a[i]]=2;
    int ans=1,cnt=0,cur=0;
    For(i,1,n)
    {
        if(vis[i])
        {
            cur+=(vis[i]==1);
            if(i==a[p]) cur++;
            continue;
        }
        ans=1ll*ans*(cnt+cur)%Mod,cnt++;
    } cout<<ans<<endl;
    return 0;
}