//=================================
// Created on: 2018/07/07 18:00:43
//=================================
#include <bits/stdc++.h>
#define show(x) cerr << #x << " = " << x << endl
using namespace std;
using ll = long long;
using ld = long double;
constexpr ll MOD = 1000000007LL;
template <typename T>
constexpr T INF = numeric_limits<T>::max() / 10;
mt19937 mt{random_device{}()};
template <typename T>
int LongestIncreasingSubsequence(const vector<T>& a)
{
    const int n = a.size();
    vector<T> dp(n, INF<T>);
    for (int i = 0; i < n; i++) { *upper_bound(dp.begin(), dp.end(), a[i]) = a[i]; }
    return lower_bound(dp.begin(), dp.end(), INF<T>) - dp.begin();
}
int main()
{
    int N;
    cin >> N;
    vector<ll> A;
    for (ll i = 0, a; i < N; i++) {
        cin >> a;
        if (a > i) { A.push_back(a - i); }
    }
    const int L = LongestIncreasingSubsequence(A);
    cout << N - L << endl;
    return 0;
}