include <bits/stdc++.h>

define ll long long

using namespace std;
ll kq=1,n,ma=1e+7,a[1000007];
int main()
{
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
for(int i=1;i<=n;i++)
{
kq=kq*(a[i]-i+1)%ma;
}
cout<<kq;
}