import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.TreeMap;

public class Main {

	static int bit[];
	static void update(int ind,int delta) {
		while (ind < bit.length) {
			bit[ind] = Math.max(bit[ind], delta);
			ind += ind & -ind;
		}
	}
	static int get(int ind) {
		int res = 0;
		while (ind > 0) {
			res = Math.max(res, bit[ind]);
			ind -= ind & -ind;
		}
		return res;
	}
	public static void main(String[]args) throws Throwable {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		boolean bad[] = new boolean[n];
		TreeMap<Integer,Integer> cord = new TreeMap();
		int arr[] = new int[n];
		for (int i = 0 ; i < n ; ++i) {
			arr[i] = sc.nextInt();
			if (arr[i] - i <= 0) {
				bad[i] = true;
			}
			arr[i] -= i;
			cord.put(arr[i], 0);
		}

		int maxVal = 1;
		for (Map.Entry<Integer,Integer> x : cord.entrySet()) {
			x.setValue(maxVal++);
		}
		int lis = 0;
		maxVal++;
		bit = new int[maxVal + 1];
		for (int i = 0 ; i < n; ++i) {
			arr[i] = cord.get(arr[i]);
		}
		for (int i = 0 ; i < n ; ++i) {
			if (bad[i]) {
				continue;
			}
			int cur = get(arr[i]) + 1;
			lis = Math.max(lis, cur);
			update(arr[i],cur);
		}

		System.out.println(n - lis);
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(String s) throws FileNotFoundException {
			br = new BufferedReader(new FileReader(new File(s)));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}

		public boolean ready() throws IOException {
			return br.ready();
		}
	}
}