#include <iostream>
#include <algorithm>
#include <cstring>
#include <sstream>
#include <map>
#include <queue>
#include <set>
#include <vector>
#include <stack>
#include <cstdio>
#include <cmath>
#define mk make_pair
#define pb push_back
#define printf printf_s
#define scanf scanf_s
using namespace std;
typedef int ll;
typedef pair<ll, ll> pos;
const ll MOD = 1000000007, N = 200001, dx[4] = { -1,1,0,0 }, dy[4] = { 0,0,-1,1 }, MIN = -72340172838, MAX = 72340172838;

ll mn(ll a, ll b) {
	if (a == -1)return b;
	if (b == -1)return a;
	return min(a, b);
}
ll gcd(ll v1, ll v2) {
	if (v1 == 0)return v2; if (v2 == 0)return v1; if (v2 > v1)return gcd(v2%v1, v1); return gcd(v1%v2, v2);
}

ll pw(ll v1, ll v2) {
	ll v3 = 1;
	while (v2 > 0) {
		if (v2 % 2)v3 = (v3*v1) % MOD;
		v1 = (v1*v1) % MOD;
		v2 /= 2;
	}
	return v3;
}

struct ab {
	ll a, b;
	bool operator<(const ab& right) const {
		return right.b*a - right.a*b < 0;
	}
};

ll hl[N],a[N],n,bt[N];

void ad(ll v1, ll v2) {
	while (v1 <= n) {
		bt[v1] =min(bt[v1],v2);
		v1 += v1 & -v1;
	}
}

ll sm(ll v1) {
	ll v2 = 0;
	while (v1 > 0) { v2 =min(v2,bt[v1]); v1 -= v1 & -v1; }
	return v2;
}

int main() {
	cin >> n; 
	for (int i = 1; i <= n; i++) { 
		cin >> a[i];
		hl[i] = a[i]-i;
	}

	sort(hl + 1, hl + n + 1);
	
	for (int i = 1; i <= n; i++) {
		ll v1 = sm(upper_bound(hl + 1, hl + n + 1, a[i]-i) - hl - 1);
		ll v2 = v1 + i - 1;
		ad(find(hl + 1, hl + n + 1, a[i]-i) - hl, v2 - i);
	}

	cout << sm(n) + n << endl;
	return 0;
}