#include <iostream>
#include <vector>
#include <algorithm>

// greedy choice:
//  always choose a optimal number, summing the largest initial score with the least final scores
//  gives an optimal solution
// safe move:
//  choose a sum that is less or equal to the current score and move ahead if so.
int naive(std::vector<unsigned int> initial_scores, std::vector<unsigned int> final_scores, int n) {
        auto max_score = final_scores[0] + initial_scores[n];
        n--;
        int score = n;

        for(int i = 1; i < final_scores.size(); i++) {
                auto cal = final_scores[i] + initial_scores[n];
                // the less value, the upper the player.
                if(cal <= max_score) {
                        n--;
                        score--;
                        if(n < 0) {
                                break;
                        }
                }
        }

        // +1 because of the index.
        // +1 because the current index points to the number before the actual one.
        return score + 2;
}

int main() {
        std::vector<unsigned int> initial_scores;
        std::vector<unsigned int> final_scores;

        int count, n;
        std::cin >> count >> n;

        for(int i = 0; i < count; i++) {
                int t;
                std::cin >> t;

                initial_scores.push_back(t);
        }

        for(int i = 0; i < count; i++) {
                int t;
                std::cin >> t;
                final_scores.push_back(t);
        }

        std::cout<<naive(initial_scores, final_scores, n-1);
        return 0;
}