#include <bits/stdc++.h>
using namespace std;
using LL = long long;
LL x[111111], a[111111];

int main(){
    
    // 1. 入力情報取得.
    int N, K;
    scanf("%d %d", &N, &K);
    K--;
    for(int i = 0; i < N; i++) scanf("%lld", &x[i]);
    for(int i = 0; i < N; i++) scanf("%lld", &a[i]);
    
    // 2. 区間の最小を計算.
    LL minL = x[K] - a[K];
    int indexL = max(0, K - 1);
    while(1){
        LL l = 1e17;
        int index = 0;
        for(int i = indexL; i >= 0; i--) if(l >= minL) l = min(l, x[i] - a[i]), index = i;
        if(l < minL) minL = l;
        if(index == 0) break;
        else           indexL = index;
    }
    
    // 3. 区間の最大を計算.
    LL maxR = x[K] + a[K];
    int indexR = min(K + 1, N - 1);
    while(1){
        LL r = -1e17;
        int index = 0;
        for(int i = indexR; i < N; i++) if(r >= maxR) r = max(r, x[i] - a[i]), index = i;
        if(r > maxR) maxR = r;
        if(index == 0) break;
        else           indexR = index;
    }
    
    // 4. 出力 ～ 後処理.
    printf("%d\n", indexR - indexL + 1);
    return 0;
    
}