#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;

int main()
{
	int N;
	cin >> N;
	ll a[100010];

	for (int i = 0; i < N; i++) {
		cin >> a[i];
	}

	ll pre = a[0],pre_ind = 1,cnt = 0;
	for (int i = 1; i < N; i++) {
		if (pre < a[i]) {
			if (a[i] - pre != 1) {
				cnt++;
			}
			cnt += i - pre_ind;
			pre = a[i];
			pre_ind = i + 1;
		}
	}
	if (pre_ind != N)cnt += N - pre_ind;

	cout << cnt<< endl;
	return 0;
}