c#include <bits/stdc++.h> using namespace std; int main(){ cin.tie(NULL); cout.tie(NULL); ios_base::sync_with_stdio(false); int N, K; cin >> N >> K; vector<int> arr; for(int i = 0; i < N; i++){ int A, B; cin >> A >> B; arr.push_back(A - B); } sort(arr.begin(), arr.end(), greater<>()); if(arr[K - 1] > 0){ cout << 0 << "\n"; }else{ cout << arr[K - 1] * -1 << "\n"; } return 0; }