#include<cstdio>

#include<cstring>

#include<iostream>

#include<algorithm>

#define M 1100

using namespace std;

typedef long long ll;

struct abcd{

    ll xx[];

    int cnt;

    abcd(int x=)

    {

        memset(xx,,sizeof xx);

        xx[]=x;

        cnt=;

    }

    ll& operator [] (int x)

    {

        return xx[x];

    }

}ans();

abcd operator *= (abcd &x,abcd &y)

{

    int i,j;

    abcd z;

    for(i=;i<=x.cnt;i++)

        for(j=;j<=y.cnt;j++)

            z[i+j-]+=x[i]*y[j],z[i+j]+=z[i+j-]/,z[i+j-]%=;

    z.cnt=x.cnt+y.cnt;

    if(!z[z.cnt])

        --z.cnt;

    x=z;

}

ostream& operator << (ostream& os,abcd &x)

{

    int i;

    printf("%lld",x[x.cnt]);

    for(i=x.cnt-;i;i--)

        printf("%08lld",x[i]);

    return os;

}

int n,m,remain,cnt[M],stack[M],top;

void Decomposition(int x,int y)

{

    int i;

    for(i=;i*i<=x;i++)

        while(x%i==)

            cnt[i]+=y,x/=i;

    if(x^)

        cnt[x]+=y;

}

void Quick_Power(int i,int y)

{

    abcd x(i);

    while(y)

    {

        if(y&)ans*=x;

        x*=x;

        y>>=;

    }

}

int main()

{

    int i,x;

    cin>>n;remain=n-;

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

    {

        scanf("%d",&x);

        if(x==-)

            ++m;

        else if(x>)

            stack[++top]=x-,remain-=x-;

    }

    for(i=;i<=n-;i++)

        Decomposition(i,);

    while(top)

    {

        for(i=;i<=stack[top];i++)

            Decomposition(i,-);

        stack[top--]=;

    }

    for(i=;i<=remain;i++)

        Decomposition(i,-);

    Decomposition(m,remain);

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

        if(cnt[i])

            Quick_Power(i,cnt[i]);

    cout<<ans<<endl;

}