#include <iostream> #include <vector> using namespace std; typedef long long ll; const ll mod = 1000007; int main() { int n; cin>>n; vector<int> v; vector<int> maxi; vector<int> dp; for(int i=0;i<n;i++) { int a; cin>>a; v.push_back(a); if(maxi.size()) { maxi.push_back(max(maxi[maxi.size()-1],a)); } else maxi.push_back(a); dp.push_back(i+1); } dp.push_back(n+1); ll brojac=1; for(int i=n-2;i>=0;i--) { brojac+=(v[i]-1)*dp[maxi[i]]; ll broj=dp[1]; for(int j=1;j<=i+1;j++) { broj+=dp[j+1]; dp[j]=broj; } } cout<<brojac<<endl; return 0; }