import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws FileNotFoundException {
		new Main().run();
	}

	void run() {
		Scanner sc = new Scanner(System.in);
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.nextInt();
		long[] A = new long[N];
		for (int i = 0; i < N; ++i) {
			A[i] = sc.nextLong() - i + N;
		}
		A = shrink(A);

		int[] dp = new int[N + 1];
		Arrays.fill(dp, Integer.MAX_VALUE / 3);
		for (int i = 0; i < N; ++i) {
			int idx = Arrays.binarySearch(dp, (int) A[i]);
			if (idx >= 0) {
				dp[idx + 1] = (int) A[i];
			} else {
				idx = -(idx + 1);
				dp[idx] = (int) A[i];
			}
		}
		int ans = 0;
		for (int i = 0; i < dp.length; ++i) {
			if (dp[i] == Integer.MAX_VALUE / 3)
				continue;
			ans = Math.max(ans, i + 1);
		}
		System.out.println(N - ans);

	}

	long[] shrink(long[] a) {
		int n = a.length;
		long[] ret = new long[n];
		long[][] x = new long[n][2];
		for (int i = 0; i < n; ++i) {
			x[i][0] = i;
			x[i][1] = a[i];
		}
		Arrays.sort(x, new Comparator<long[]>() {
			@Override
			public int compare(long[] o1, long[] o2) {
				return Long.compare(o1[1], o2[1]);
			}
		});
		int p = 1;
		for (int i = 0; i < n; ++i) {
			ret[(int) x[i][0]] = p;
			if (i + 1 < n && x[i][1] != x[i + 1][1])
				++p;
		}
		return ret;
	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}