#include <bits/stdc++.h>
using namespace std;

// Longest Increasing Subsequence の長さを返す。「正整数」で、広義単調増加。
template <typename T>
auto LIS_weak_size(const vector<T> &vs){
    const auto n = vs.size();
    constexpr T inf = numeric_limits<T>::max();
    vector<T> A(n + 1, inf);
    for (auto v : vs) if (v > 0) A[distance(A.begin(), upper_bound(A.begin(), A.end(), v))] = v;
    return distance(A.begin(), lower_bound(A.begin(), A.end(), inf));
}

int main() {
    int N;
    cin >> N;
    vector<long long> As(N);
    for (auto &a : As) cin >> a;
    for (int i = 0; i < N; ++i) As[i] -= i;
    cout << N - LIS_weak_size(As) << endl;
    return 0;
}