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

public class Main {
 	public static void main(String[] args){
		FastScanner scanner = new FastScanner();
		int n = scanner.nextInt();
		int k = scanner.nextInt()-1;
		long[] x = new long[n];
		long[] a = new long[n];
		for(int i = 0; i < n; i++){
			x[i] = scanner.nextLong();
		}
		for(int i = 0; i < n; i++){
			a[i] = scanner.nextLong();
		}
		long min = x[k]-a[k];
		long max = x[k]+a[k];
		for(int j = 0; j < 100; j++){
			for(int i = k; i >= 0; i--){
				if(x[i] >= min){
					min = Math.min(min,x[i]-a[i]);
					max = Math.max(max,x[i]+a[i]);
				}
			}
			for(int i = k; i < n; i++){
				if(x[i] <= max){
					min = Math.min(min,x[i]-a[i]);
					max = Math.max(max,x[i]+a[i]);
				}
			}
		}	

		int start = 0;
		int end = n-1;
		for(int i = 0; i < n; i++){
			if(x[i] >= min){
				start = i;
				break;
			}
		}
		for(int i = n-1; i >= 0; i--){
			if(x[i] <= max){
				end = i;
				break;
			}
		}
		System.out.println(end-start+1);
	}
	public static int upperBound(long[] array, long value) {
			 int low = 0;
			 int high = array.length;
			 int mid;
			 while( low < high ) {
					 mid = ((high - low) >>> 1) + low; // (high + low) / 2
					 if( array[mid] <= value ) {
							 low = mid + 1;
					 } else {
							 high = mid;
					 }
			 }
			 return low;
	 }
	 public static final int lowerBound(final long[] arr, final long value) {
    	int low = 0;
    	int high = arr.length;
    	int mid;
    	while (low < high){
        	mid = ((high - low) >>> 1) + low;    //(low + high) / 2 (オーバーフロー対策)
        	if (arr[mid] < value) {
          	low = mid + 1;
        	} else {
            high = mid;
        	}
    	}
    	return low;
		}
	private static 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;}
		public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; 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() {
				long nl = nextLong();
				if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
				return (int) nl;
		}
		public double nextDouble() { return Double.parseDouble(next());}
	}
}