#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<long long> VL;
typedef vector<VL> VVL;
typedef long long LL;
#define all(a) (a).begin(), (a).end()
#define Yes(n) cout << ((n) ? "Yes" : "No"  ) << endl
#define ALL(a)  (a).begin(),(a).end()



int main() {
  int n; cin>>n;
  int A[n];
  rep(i,n){cin>>A[i];}
  LL dp[n][A[0]+1]={};
  rep(i,A[n-1]){dp[n-1][i+1]=1;}
  for(int i=n-2;i>=0;i--){
    dp[i][A[i]]=1+dp[i+1][A[i]];
    for(int j=A[i]-1;j>=1;j--){
      dp[i][j]=dp[i][j+1]+dp[i+1][j];
    }
  }
  LL ans=1;
  for(int i=1;i<=A[0];i++){ans+=dp[0][i];}
  cout<<ans<<endl;
}