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

	}

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

	int gt(int[] A, int key) {
		int ok = A.length;
		int ng = -1;
		while (ok - ng > 1) {
			int m = (ok + ng) / 2;
			if (A[m] <= key) {
				ng = m;
			} else {
				ok = m;
			}
		}
		return ng + 1;
	}

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

}