这道题里面不用保存 inva[i] ，而且还卡常。事实证明快读快到飞起，

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

const int MAXN=5000005;

int a[MAXN];
ll pp[MAXN];

inline int qpow(ll x,int n,int p){
    ll res=1;
    while(n){
        if(n&1){
            res=res*x;
            if(res>=p)
                res%=p;
        }
        x=x*x;
        if(x>=p)
            x%=p;
        n>>=1;
    }
    return res;
}

inline int read(){
    char c=getchar();
    int x=0;
    while(c<'0'||c>'9')
        c=getchar();
    while(c>='0'&&c<='9'){
        x=x*10+c-'0';
        c=getchar();
    }
    return x;
}

void solve(){
    int n=read(),p=read(),k=read();
    for(int i=1;i<=n;i++)
        a[i]=read();
    pp[0]=1;
    for(int i=1;i<=n;i++){
        pp[i]=pp[i-1]*a[i];
        if(pp[i]>=p)
            pp[i]%=p;
    }

    int invk=qpow(k,p-2,p);
    ll ans=0,ki=qpow(k,n,p);
    ll invpp=qpow(pp[n],p-2,p);

    for(int i=n;i>=1;i--){
        ll inva=invpp*pp[i-1];
        if(inva>=p)
            inva%=p;

        ans+=ki*inva;
        if(ans>=p)
            ans%=p;

        ki*=invk;
        if(ki>=p)
            ki%=p;

        invpp*=a[i];
        if(invpp>=p)
            invpp%=p;
    }

    printf("%lld\n",ans);
    return;
}

int main() {
#ifdef Yinku
freopen("Yinku.in","r",stdin);
#endif // Yinku
    solve();
    return 0;
}