#include <bits/stdc++.h>

using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using ll = long long;
using vi = vector<ll>;
using vii = vector<vi>;
using pii = std::pair<ll,ll>;

#define rep(i,j,k) for(ll i=ll(j); i<ll(k); i++)
#define REP(i,j,k) for(ll i=ll(j); i<=ll(k); i++)
#define per(i,j,k) for(ll i=ll(j); i>=ll(k); i--)
#define ln "\n"
#define pb emplace_back
#define mp std::make_pair
#define all(a) a.begin(),a.end()
#define mtp std::make_tuple

constexpr ll inf = (1ll<<60);
constexpr ll mod = (1e6)+3;

int main(){
    cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    ll N; cin >> N;
    vi H(N);
    rep(i,0,N) cin >> H[i];
    ll ans = 0;
    vector<bool> flag(N,1);
    while(true){
        ll min = inf;
        rep(i,0,N){
            if(flag[i]) min = std::min(min, H[i]);
        }
        if(min == inf) break;
        rep(i,0,N){
            if(!flag[i] || min != H[i]) continue;
            ll l = inf, r = inf;
            rep(j,0,i){
                if(H[j] > H[i]) l = std::min(l, H[j]);
            }
            rep(j,i+1,N){
                if(H[j] > H[i]) r = std::min(r, H[j]);
            }
            if(l == inf || r == inf){
                flag[i] = false;
            }
            else{
                ans += l+r+H[i];
                H[i]++;
            }
            break;
        }
    }
    cout << ans << ln;
}