#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
#endif
using ll = long long;
using ld = long double;
const ll INF = 1ll<<60;
const ld EPS = 1.0/1e9;
#define endl "\n"
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()
#define del(x) sort(all(x)); x.erase(unique(all(x)),x.end());

int main(){
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ll n; cin >> n;
  ll ans=n*(n+1)/2;
  rep(i,1,n+1){
    ll p; cin >> p;
    if(p==n) ans-=i*2;
  }
  ans=max(ans,0ll);
  cout << ans << endl;
}