#include<bits/stdc++.h>
#define P 1000000007
#define ll long long
using namespace std;
const int N=105;
int n,m,k,s,t,H[N],mi;
ll f[N][1005],ans;
void calc(int k){
	memset(f,0,sizeof(f));
	f[1][k]++;
	for (int i=1;i<n;++i){
		int sum=0;
		for (int j=k;j<=H[i];++j){
			sum=(sum+f[i][j])%P;
			if (k<=H[i+1]-(j-k)){
				(f[i+1][k]+=sum)%=P;
				(f[i+1][H[i+1]-(j-k)+1]-=sum)%=P;
			}
		}
	}
	ans=(ans+f[n][k])%P;
}
int main(){
    cin>>n;mi=0x3f3f3f3f;
    for (int i=1;i<=n;++i) cin>>H[i],mi=min(mi,H[i]);
    if (n&1) for (int i=0;i<=mi;++i) 
				calc(i);
    else calc(0);
    cout<<(ans+P)%P;
}