import java.io.OutputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.StringTokenizer; import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.InputStream; /** * Built using CHelper plug-in * Actual solution is at the top * * @author Chiaki.Hoshinomori */ public class Main { public static void main(String[] args) { InputStream inputStream = System.in; OutputStream outputStream = System.out; InputReader in = new InputReader(inputStream); PrintWriter out = new PrintWriter(outputStream); Task484 solver = new Task484(); solver.solve(1, in, out); out.close(); } static class Task484 { long[][][] dp; long[] A; public void solve(int testNumber, InputReader in, PrintWriter out) { int n = in.nextInt(); A = in.nextLongArray(n); dp = new long[n][][]; for (int i = 0; i < n; i++) { dp[i] = new long[n][]; for (int j = 0; j < n; j++) { dp[i][j] = new long[2]; dp[i][j][0] = dp[i][j][1] = -1; } } long ret = 1l << 60; for (int i = 0; i < n; i++) { ret = Math.min(ret, solve(i, i, 0)); } out.println(ret); } private long solve(int l, int r, int s) { if (dp[l][r][s] >= 0) return dp[l][r][s]; long ret = 1l << 60; if (l == 0 && r == A.length - 1) { if (s == 0) dp[l][r][s] = A[l]; else dp[l][r][s] = A[r]; return dp[l][r][s]; } if (s == 0) { if (l > 0) { ret = Math.min(ret, solve(l - 1, r, 0) + 1); } if (r + 1 < A.length) { ret = Math.min(ret, solve(l, r + 1, 1) + r - l + 1); } ret = Math.max(ret, A[l]); } else { if (l > 0) { ret = Math.min(ret, solve(l - 1, r, 0) + r - l + 1); } if (r + 1 < A.length) { ret = Math.min(ret, solve(l, r + 1, 1) + 1); } ret = Math.max(ret, A[r]); } return dp[l][r][s] = ret; } } static class InputReader { public BufferedReader reader; public StringTokenizer tokenizer; public InputReader(InputStream stream) { reader = new BufferedReader(new InputStreamReader(stream), 32768); tokenizer = null; } public String next() { while (tokenizer == null || !tokenizer.hasMoreTokens()) { try { tokenizer = new StringTokenizer(reader.readLine()); } catch (IOException e) { throw new RuntimeException(e); } } return tokenizer.nextToken(); } public int nextInt() { return Integer.parseInt(next()); } public long nextLong() { return Long.parseLong(next()); } public long[] nextLongArray(int n) { long[] r = new long[n]; for (int i = 0; i < n; i++) { r[i] = nextLong(); } return r; } } }