#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
const long long MOD = 1000000007;
const long long INF = 9999999999999999;
using ll = long long;
using mint = modint1000000007;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
int main(){
  ll N;
  cin>>N;
  vector<ll> A(N);
  rep(i,N){
    cin>>A[i];
  }
  ll ans = 0;
  rep(i,N){
    if(A[i] == i+1){
      continue;
    }
    else{
      ll temp = A[i];
      A[i] = i+1;
      for(int k = i+1;k<N;k++){
        if(A[k]<temp && A[k]>=(i+1)){
          A[k]++;
          ans++;
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}