Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<cstring>

using namespace std;

typedef long long ll;

ll MOD;

ll m,n;

#define MAXN 6

ll w[MAXN];

ll tot = 0,divi[100000],times[100000];

ll sumw = 0;

void dev()

{

    ll k = MOD;

    for(ll i = 2;i <= k;++i)

    {

        if(k % i == 0)

        {

            divi[++tot] = i;

            times[tot] = 1;

            while(k % i == 0)

            {

                times[tot] *= i;

                k /= i;

            }

        }

    }

    return;

}

ll power(ll a,ll b,ll mod)//a ^ b % mod

{

    ll res = 1;

    while(b > 0)

    {

        if(b & 1)res = res * a % mod;

        a = a * a % mod;

        b = b >> 1;

    }

    return res;

}

ll fac(ll n,ll p,ll pr)//n! % pr

{

    if(n == 0)return 1;

    ll res = 1;

    for(ll i = 2;i <= pr;++i)

    {

        if(i % p != 0)

        {

            res = res * i % pr;

        }

    }

    res = power(res,n / pr,pr);

    ll r = n % pr;

    for(ll i = 2;i <= r;++i)

    {

        if(i % p != 0)

        {

            res = res * i % pr;

        }

    }

    res = res * fac(n / p,p,pr) % pr;

    return res;

}

ll exgcd(ll a,ll b,ll &x,ll &y)//ax + by = gcd(a,b)

{

    if(b == 0)

    {

        x = 1;y = 0;

        return a;

    }

    ll t = exgcd(b,a % b,x,y);

    ll k = x;

    x = y;

    y = k - (a / b) * y;

    return t;

}

ll inv(ll a,ll n)//a * a^{-1} = 1 (mod n)

{

    ll x,y;

    ll t = exgcd(a,n,x,y);

    x = (x % n + n) % n;

    return x;

}

ll lucas(ll n,ll m,ll p,ll pr)

{

    if(n < m)return 0;

    ll c = 0;

    for(ll i = n;i > 0;i /= p)c += i / p;

    for(ll i = m;i > 0;i /= p)c -= i / p;

    for(ll i = n - m;i > 0;i /= p)c -= i / p;

    ll res = fac(n,p,pr) * inv(fac(m,p,pr),pr) % pr * inv(fac(n - m,p,pr),pr) % pr * power(p,c,pr) % pr;

    return res;

}

ll CRT(ll n,ll m)

{

    ll ans = 0;

    for(int i = 1;i <= tot;++i)

    {

        ans = (ans + lucas(n,m,divi[i],times[i]) * inv(MOD / times[i],times[i]) % MOD * (MOD / times[i]) % MOD) % MOD;

    }

    return ans;

}

int main()

{

    scanf("%lld",&MOD);

    scanf("%lld%lld",&m,&n);

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

    {

        scanf("%lld",&w[i]);

        sumw += w[i];

    }

    if(sumw > m){puts("Impossible");return 0;}

    if(MOD == 1){puts("0");return 0;}

    dev();

    ll ans = 1;

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

    {

        ans = ans * CRT(m,w[i]) % MOD;

        m -= w[i];

    }

    cout << ans << endl;

    return 0;

}