5
1 8 1 7 9
 4
6 7 4 5
 5
36 37 6 18 36
 3
5 1 3
 200
2 1 1 1 2 1 2 1 1 1 2 1 2 2 2 1 1 2 1 2 1 1 1 2 2 1 2 1 1 2 1 1 1 2 1 1 2 2 2 2 2 2 2 2 2 2 1 2 2 1 2 1 2 2 1 1 2 2 2 2 2 2 2 1 1 1 2 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 1 1 2 2 1 2 2 1 2 2 1 1 2 1 1 1 1 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 2 1 2 2 2 1 1 2 1 2 2 1 2 2 2 1 1 2 2 1 2 1 1 2 2 1 2 1 2 1 2 2 2 1 1 2 2 1 1 2 1 1 1 2 2 2 1 2 2 2 1 2 1 1 1 1 2 1 2 1 2 1 1 1 2 2 2 1 2 1 1 2 2 1 1 1 1 1 2 2 2 1 2 2
 10
104105246720 52052623360 213207545282560 426415090565120 6354080 832841973760 26650943160320 6506577920 50832640 832841973760
 3
9 4 4
 10
3 3 3 3 3 3 3 3 3 3
 100
24 33 88 55 4 24 19 19 63 90 9 47 24 74 21 43 20 100 58 15 36 66 13 4 9 51 24 96 50 27 100 41 92 9 67 94 17 11 98 24 72 57 96 85 50 9 45 41 63 76 80 59 25 67 21 84 88 15 62 60 79 65 5 66 1 85 92 100 61 75 44 96 53 97 2 28 83 42 60 42 34 73 44 99 58 46 75 100 75 55 35 52 93 80 69 75 50 67 100 77
 200
1 2 1 2 2 1 2 2 2 1 1 1 2 2 1 2 2 1 2 1 1 2 1 2 1 2 2 1 2 2 1 2 1 2 1 2 1 2 2 1 1 1 1 2 1 1 2 2 1 2 1 1 2 2 2 1 2 1 1 1 1 1 1 1 2 1 2 2 2 2 2 2 1 1 1 2 2 2 2 2 1 2 1 2 1 2 2 2 1 1 1 1 2 1 1 1 2 2 1 2 1 1 1 2 2 1 1 2 1 2 1 2 1 1 1 2 2 2 1 1 1 2 2 2 1 2 1 2 2 1 2 2 2 1 1 1 1 1 2 2 2 2 2 2 1 1 1 2 1 1 1 1 2 1 2 2 2 2 1 2 2 1 1 1 1 1 2 1 2 2 2 2 1 1 1 2 1 2 1 2 1 1 2 1 1 2 1 2 1 1 1 1 2 1 2 1 1 1 2 2
 4
3 1 5 5
 200
2 2 3 2 1 2 1 2 6 1 6 2 6 1 2 6 5 1 3 6 2 2 4 4 5 5 3 2 2 3 4 2 1 2 2 5 3 6 3 4 5 5 2 2 2 4 6 6 4 4 5 6 6 1 6 6 5 5 6 3 6 2 2 4 1 5 5 5 5 4 2 6 1 2 1 2 2 3 5 5 5 1 5 4 2 1 3 2 5 5 6 4 2 5 2 5 2 2 2 4 3 5 2 2 1 2 1 6 4 3 2 3 6 1 5 5 4 1 2 2 5 3 1 3 6 2 6 4 3 3 1 3 3 5 2 1 3 4 6 4 3 6 3 4 3 1 3 4 6 3 4 1 5 3 5 4 2 1 6 1 6 5 4 6 6 2 3 6 5 2 6 4 5 1 2 5 4 1 5 2 5 5 4 3 1 6 3 2 5 2 2 3 3 1 1 3 6 6 6 2
 200
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

3
 3
 2
 1
 33
 8
 1
 0
 91
 30
 2
 122
 0

import java.io.*;
import java.util.Scanner;

/**
 * User: Oleksiy Pylypenko
 * Date: 1/6/13
 * Time: 1:46 PM
 */
public class D {
    static boolean debug = !"true".equalsIgnoreCase(System.getProperty("ONLINE_JUDGE"));
    private Scanner in;
    private PrintWriter out;

    private void solve() throws IOException {
        int n = in.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = in.nextLong();
        }

        int intv = 0;
        int s = 0;
        for (int i = 1; i < n; i++) {
            if (!isLucky(a[i-1], a[i])) {
                intv++;
            } else {
                s += (intv + 1) / 2;
                intv = 0;
            }
        }
        s += (intv + 1) / 2;
        out.println(s);
    }

    private boolean isLucky(long x, long y) {
        return (2 * x - y * y + y) % (2 * y) == 0;
    }

    public static void main(String[] args) throws IOException {
        new D().exec();
    }

    private void exec() {
        if (debug) {
            try {
                System.setIn(new FileInputStream(getClass().getName() + ".in"));
            } catch (FileNotFoundException e) {
                System.out.println(e);
                System.exit(1);
            }
        }
        in = new Scanner(new InputStreamReader(System.in));
        out = new PrintWriter(System.out, true);

        try {
            if (debug) {
                while (in.hasNext()) {
                    solve();
                }
            } else {
                solve();
            }
        } catch (IOException e) {
            if (debug) {
                System.out.println(e);
                System.exit(1);
            }
        } finally {
            out.close();
            in.close();
        }
    }

}
