#include <bits/stdc++.h>
#define ll long long
#define rep(i,m,n) for(int i=(m); i<=(n); i++)
#define reb(i,m,n) for(int i=(m); i>=(n); i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define MP make_pair
#define fs first
#define se second
#define bit(msk, i) ((msk >> i) & 1)
#define iter(id, v) for(auto id : v)
#define pb push_back
#define SZ(v) (ll)v.size()
#define ALL(v) v.begin(),v.end()
using namespace std;
mt19937_64 rd(chrono :: steady_clock :: now ().time_since_epoch().count());
ll Rand (ll l, ll r) { return uniform_int_distribution<ll> (l, r) (rd); }
const int N = 2e5 + 7;
const int Mod = 1e6 + 3;///lon
const ll INF = 1e18 + 7;
const ll BASE = 137;
const int szBL = 250;
int n;
int a[N];
struct Segment_Tree {
int m;
pii st[N << 2];
void build (int id, int l, int r) {
if (l == r) {
st[id] = {a[l], 1};
return;
}
int mid = l + r >> 1;
build (id << 1, l, mid);
build (id << 1 | 1, mid + 1, r);
st[id].fs = max(st[id << 1].fs, st[id << 1 | 1].fs);
st[id].se = st[id << 1].se + st[id << 1 | 1].se;
}
void init (int n) {
m = n;
build (1, 1, m);
}
void update (int id, int l, int r, int pos) {
if (l > pos || r < pos) return;
if (l == r) {
st[id] = {0, 0};
return;
}
int mid = l + r >> 1;
update (id << 1, l, mid, pos);
update (id << 1 | 1, mid + 1, r, pos);
st[id].fs = max(st[id << 1].fs, st[id << 1 | 1].fs);
st[id].se = st[id << 1].se + st[id << 1 | 1].se;
}
int get (int id, int l, int r, int u, int v) {
if (l > v || r < u) return 0;
if (l >= u && r <= v) return st[id].fs;
int mid = l + r >> 1;
return max (get (id << 1, l, mid, u, v), get (id << 1 | 1, mid + 1, r, u, v));
}
int cnt (int id, int l, int r, int u, int v) {
if (l > v || r < u) return 0;
if (l >= u && r <= v) return st[id].se;
int mid = l + r >> 1;
return cnt (id << 1, l, mid, u, v) + cnt (id << 1 | 1, mid + 1, r, u, v);
}
void update (int pos) {
update (1, 1, m, pos);
}
int get (int u, int v) {
return get (1, 1, m, u, v);
}
int cnt (int u, int v) {
return cnt (1, 1, m, u, v);
}
}ST;
void solution () {
cin >> n;
rep (i, 1, n) cin >> a[i];
ST.init(n);
ll res = 0;
reb (i, n, 1) {
int pos; {
int lf = 1, rt = n;
while (lf < rt) {
int mid = lf + rt + 1>> 1;
if (ST.get(mid, n) >= i) lf = mid;
else rt = mid - 1;
}
if (ST.get(lf, n) < i) pos = -1;
else pos = lf;
}
if (pos == -1) {
cout << -1 <<"\n";
return;
}
res += ST.cnt(pos, n) - 1;
ST.update(pos);
}
cout << res <<"\n";
}
#define file(name) freopen(name".inp","r",stdin); \
freopen(name".out","w",stdout);
main () {
// file("c");
ios_base :: sync_with_stdio(false); cin.tie(0); cout.tie(0);
int num_Test = 1;
// cin >> num_Test;
while (num_Test--)
solution();
}
/*
no bug challenge +12
*/
