#include <bits/stdc++.h>
using namespace std;
int main(void){
    // Your code here!
    int N; cin >> N;
    assert(1 <= N && N <= 100000);
    int K; cin >> K;
    assert(1 <= K && K <= N);
    
    vector<long long> X(N+2);
    vector<long long> A(N+2);
    X[0] = -1000000000000000000;
    X[N+1] = 1000000000000000000;
    
    for (int i = 1; i <= N; i++) {
        cin >> X[i];
        assert(-100000000000000000 <= X[i] && X[i] <= 100000000000000000);
        if (2 <= i) {
            assert(X[i-1] < X[i]);
        }
    }
    for (int i = 1; i <= N; i++) {
        cin >> A[i];
        assert(0 < A[i] && A[i] < 100000000000000000);
    }
    
    long long l = X[K] - A[K];
    long long r = X[K] + A[K];
    long long rFrog = K+1;
    long long lFrog = K-1;
    int flag = 1;
    while (flag) {
        flag = 0;
        if (X[rFrog] <= r) {
            r = max(X[rFrog] + A[rFrog], r);
            l = min(X[rFrog] - A[rFrog], l);
            rFrog += 1;
            flag = 1;
        }
        if (l <= X[lFrog]) {
            r = max(X[lFrog] + A[lFrog], r);
            l = min(X[lFrog] - A[lFrog], l);
            lFrog -= 1;
            flag = 1;
        }
    }
    
    cout << rFrog - lFrog - 1 << endl;
    return 0;
}