#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){int X=0;bool f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=0;ch=getchar();}
while(ch>='0'&&ch<='9')X=(X<<1)+(X<<3)+ch-'0',ch=getchar();if(f) return X;return ~(X-1);}//快读
signed main(){
	int n=read();
	int ss=n+1,mod=1e9+7;
	while(n--) ss=(ss+n-read())%mod*n/2+2;
	cout<<ss;
	return 0;
}

这就40分了！！！code