import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
T[] RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[][] RDA2(T = long)(size_t n, T[] fix = []) { auto r = new T[][](n); foreach (i; 0..n) { r[i] = readln.chomp.split.to!(T[]); foreach (j, e; fix) r[i][j] += e; } return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * y / gcd(x, y); }

long mod = 10^^9 + 7;
//long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{
	auto N = RD;
	auto K = RD-1;
	auto X = RDA;
	auto A = RDA;
	long xl = X[K] - A[K], xr = X[K] + A[K];
	long l = K, r = K;
	bool changed = true;
	while (changed)
	{
		changed = false;
		foreach (i; r+1..N)
		{
			if (X[i] <= xr)
			{
				r = i;
				xr = max(xr, X[i] + A[i]);
				xl = min(xl, X[i] - A[i]);
				changed = true;
			}
			else
				break;
		}
		foreach_reverse (i; 0..l)
		{
			if (X[i] >= xl)
			{
				l = i;
				xr = max(xr, X[i] + A[i]);
				xl = min(xl, X[i] - A[i]);
				changed = true;
			}
			else
				break;
		}
	}

	writeln(r-l+1);
	stdout.flush();
	debug readln();
}