#include using namespace std; #if __has_include() #include 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 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; }