1.10

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e6;
int n,m,p;
inline int read()
{
    int s = 0,w = 1;char ch = getchar();
    while(ch<'0'||ch>'9'){ if(ch == '-') w = -1;ch = getchar();}
    while(ch>='0'&&ch<='9'){ s = s*10+ch-'0';ch = getchar();}
    return s*w;
}
inline int qpow(int a, int b,int p)
{
    int ans=1;a%=p;
    while(b)
    {
        if(b&1) ans=ans*a%p;
        a=a*a%p;
        b>>=1;
    }
    return ans;
}
inline void exgcd(int a,int b,int &x,int &y)
{
    if(!b)
        return (void)(x=1,y=0);
    exgcd(b,a%b,x,y);
    int tmp=x;x=y;y=tmp-a/b*y;
}
inline int inv(int a,int p)
{
    int x,y;
    exgcd(a,p,x,y);
    return (x+p)%p;
}
inline int fac(int n,int p,int pk)
{
    if(n==0) return 1;
    int ans=1,mo=1;
    for(int i=1;i<=pk;++i)
        if(i%p)
            ans=ans*i%pk;
    ans=qpow(ans,n/pk,pk);
    for(int i=pk*(n/pk);i<=n;++i)
        if(i%p)
            mo=mo*(i%pk)%pk;
    return ans%pk*fac(n/p,p,pk)*mo%pk;
}
inline int G(int n,int p)
{
    if(n<p) return 0;
    return G(n/p,p)+(n/p);
}
inline int C(int n,int m,int p,int pk)
{
    int f1=fac(n,p,pk),f2=inv(fac(m,p,pk),pk),f3=inv(fac(n-m,p,pk),pk);
    int b=qpow(p,G(n,p)-G(m,p)-G(n-m,p),pk);
    return f1*f2%pk*f3%pk*b%pk;
}
int a[N],b[N];
int cnt;
inline int exlucas(int n,int m,int p)
{
    int P=p,tot=0;
    int Genshin=sqrt(p);
    for(int i=2;i<=Genshin;i++)
    {
        if(!(P%i))
        {
            int pk=1;
            while(!(P%i))
            {
                pk*=i;P/=i;
            }
            a[++tot]=pk;b[tot]=C(n,m,i,pk);
        }
    }
    if(P!=1)
    {
        a[++tot]=P;b[tot]=C(n,m,P,P);
    }
    int ans=0;
    for(int i=1;i<=tot;++i)
    {
        int M=p/a[i],t=inv(M,a[i]);
        ans=(ans+b[i]*M%p*t%p)%p;
    }
    return ans;
}
int w[N],sum,ans=1;
signed main()
{
    int p=read(),n=read(),m=read();
    for(int i=1;i<=m;++i) {w[i]=read(),sum+=w[i];}
    if(sum>n) {cout<<"Impossible";return 0;}
    for(int i=1;i<=m;++i)
    {
        ans=ans*exlucas(n,w[i],p)%p;
        n-=w[i];
    }
    cout<<ans<<endl;
}