import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.math.BigInteger; import java.util.Arrays; import java.util.NoSuchElementException; public class Main { public static void main(String[] args) { new Main().run(); } void run() { FastScanner sc=new FastScanner(); int N=sc.nextInt(); int L=sc.nextInt(); int[] X=new int[N]; for (int i=1;i=L) { System.out.println(-1); return; } } int ans=0; long center_of_gravity=0; for (int i=X.length-1;i>=1;--i) { center_of_gravity+=X[i]; long denominator=(X.length-i); long dx1=Math.abs(center_of_gravity-denominator*X[i]); long dx2=Math.abs(center_of_gravity-denominator*X[i-1]); if (2*dx1>=denominator*L||2*dx2>=denominator*L) ++ans; } System.out.println(ans); } void tr(Object...objects) {System.out.println(Arrays.deepToString(objects));} } class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; }else{ ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;} private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;} private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;} public boolean hasNext() { skipUnprintable(); return hasNextByte();} public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while(true){ if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; }else if(b == -1 || !isPrintableChar(b)){ return minus ? -n : n; }else{ throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { return (int)nextLong(); } }