/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author aajisaka
 */


#include<bits/stdc++.h>

using namespace std;

void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

#define SPEED ios_base::sync_with_stdio(false);cin.tie(nullptr)
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define all(v) v.begin(), v.end()
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

using ll = long long;
using ull = unsigned long long;
using P = pair<ll, ll>;

constexpr long double PI = 3.14159265358979323846264338327950288L;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

class No929 {
public:
    void solve(istream& cin, ostream& cout) {
      SPEED;
      int n; cin >> n;
      set<P> st;
      rep(i, n) {
        int b; cin >> b;
        if (b > 0) {
          st.emplace(i, b);
        }
      }
      ll ret = 0;

      rep(i, n) {
        auto it = st.lower_bound(P(i, 0));
        if (it != st.end()) {
          auto p = (*it);
          if (p.first == i) {
            st.erase(it);
            if (p.second > 1) {
              st.emplace(p.first, p.second - 1);
            }
            continue;
          }
        }

        if (it != st.begin()) {
          it--;
        }
        auto p2 = (*it);
        ret += abs(i - p2.first);
        st.erase(it);
        if (p2.second > 1) {
          st.emplace(p2.first, p2.second - 1);
        }
      }
      cout << ret << endl;

    }
};

signed main() {
  No929 solver;
  std::istream& in(std::cin);
  std::ostream& out(std::cout);
  solver.solve(in, out);
  return 0;
}