T147T2

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll long long
#define ull unsigned long long

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c)){x=x*10+c-'0';gc;}x*=k;
}

const int N=1e5+7;

int n;
ll p,A,B;

inline ll add(ll a,ll b){
    return (a+=b)>=p?a-p:a;
}

inline ll sub(ll a,ll b){
    return (a-=b)<0?a+p:a;
}

inline ll mul(ll a,ll b){
    ll ans=0;
    if(a<b)swap(a,b);
    while(b){
        if(b&1)ans=add(ans,a);
        a=add(a,a);
        b>>=1;
    }
    return ans;
}

inline ll qpow(ll a,ll b){
    ll ans=1;
    while(b){
        if(b&1)ans=mul(ans,a);
        a=mul(a,a);
        b>>=1;
    }
    return ans;
}

ll w;

struct comp{
    ll x,y;
    inline comp(ll a,ll b):x(a),y(b){}
};

inline comp operator + (const comp &a,const comp &b){
    return comp(add(a.x,b.x),add(a.y,b.y));
}

inline comp operator * (const comp &a,const comp &b){
    return comp(add(mul(a.x,b.x),mul(w,mul(a.y,b.y))),add(mul(a.x,b.y),mul(a.y,b.x)));
}

inline comp qpow(comp a,ll b){
    comp ans(1,0);
    while(b){
        if(b&1)ans=ans*a;
        a=a*a;
        b>>=1;
    }
    return ans;
}

inline ull rnd0(){
    return rand();
}

inline ull rnd1(){
    return (rnd0()<<16)|rnd0();
}

inline ull rnd2(){
    return (rnd1()<<32)|rnd0();
}

inline ull rnd(ll l,ll r){
    return l+rnd2()%(r-l+1);
}

inline ll check(ll x){
    return qpow(x,(p-1)/2);
}

inline ll Sqrt(ll x){
    if(x==0)return 0;
    if(check(x)==p-1)return -1;
    ll t=rnd(1,p-1);
    while(1){
        w=sub(mul(t,t),x);
        if(check(w)==p-1)return qpow(comp(t,1),(p+1)/2).x;
        t=rnd(1,p-1);
    }
}

int fa[N];
ll a[N];
vector<int>G[N];

ll ans,rt,t1,t2;
map<ll,int>cnt;

void dfs(int x){
    if(a[x]==0)ans+=cnt[0];
    else if(~rt){
        ans+=cnt[mul(a[x],t1)];
        if(t2!=t1)ans+=cnt[mul(a[x],t2)];
    }
    cnt[a[x]]++;
    for(int i=0;i<G[x].size();++i){
        dfs(G[x][i]);
    }
    cnt[a[x]]--;
}

int main(){
    freopen("mikan.in","r",stdin);
    freopen("mikan.out","w",stdout);
    r(n),r(p),r(A),r(B);
    for(int i=1;i<=n;++i)r(a[i]);
    for(int i=2;i<=n;++i){
        r(fa[i]);
        G[fa[i]].push_back(i);
    }
    rt=Sqrt(sub(mul(A,A),4*B%p));
    (B*=2)%=p;
    B=qpow(B,p-2);
    t1=mul((p-A+rt)%p,B);
    t2=mul((2*p-A-rt)%p,B);
    dfs(1);
    printf("%lld\n",ans);
}
/*
5 7 5 6
4 6 2 2 3
1 1 2 2

*/