import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.io.OutputStream;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
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);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int N = in.nextInt();
            int[] b = new int[N+1];
            int sum = 0;
            for(int i=1; i<=N; i++){
                b[i] = in.nextInt();
                sum += b[i];
            }
            int res=0;
            int min=1000000;
            for(int i=1; i<=10000; i++){
                if(i%2==0) continue;
                int p = ((i+1)/2)*((i+1)/2);
                if(sum<p) continue;
                for(int j=1; j<=Math.min((i+1)/2,N);j++){
                    res+=Math.max(0,b[j]-j);
                }
                int flag=1;
                for(int j=(i+3)/2; j<=Math.min(i,N); j++){
                    res+=Math.max(0,b[j]-((i+1)/2-flag));
                    flag++;
                }
                for(int j=i+1; j<=N; j++){
                    res+=b[j];
                }
                if(res<min) min=res;
                res=0;
            }
            out.println(min);
        }
    }

    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());
        }

    }
}