#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define REP1(i, n) for(int i=1; i<=(n); i++)
#define RREP1(i, n) for(int i=(n); i>=1; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/
#if DEBUG
#define SIZE 100
#else
#define SIZE 123450
#endif

int N,K,X[SIZE],A[SIZE];

void solve() {
    cin>>N>>K;
    K--;
    REP(i,N)cin>>X[i];
    REP(i,N)cin>>A[i];
    int mii = K;
    int mi = X[K]-A[K];
    int mai = K;
    int ma = X[K]+A[K];
    while(1) {
        if (mii && mi <= X[mii-1]) {
            mii--;
            ma = max(ma, X[mii]+A[mii]);
            mi = min(mi, X[mii]-A[mii]);
        }
        else if (mai < N-1 && X[mai+1] <= ma) {
            mai++;
            ma = max(ma, X[mai]+A[mai]);
            mi = min(mi, X[mai]-A[mai]);
        }
        else break;
    }
    cout << (mai-mii+1) << endl;
}