// Mahmud Isali
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
// #include <bits/extc++.h>
using namespace std;
// using namespace __gnu_pbds;
// #define int long long
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define pb push_back
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
const long long INF = 1e18, MOD = 1e9 + 9, N = 5e5 + 10;
void solve() {
int n,k;
cin >> n >> k;
int ans = 0;
vector<pair<int,int>> v(n + 1, {0,0});
for(int i = 1; i <= n; i++) {
cin >> v[i].F >> v[i].S;
}
for(int l = 1; l <= 105; l++) {
for(int r = l + 1; r <= 105; r++) {
int cnt = 0;
for(int i = 1; i <= n; i++) {
if(v[i].F <= l && v[i].S > r) cnt++;
}
if(cnt >= k) ans = max(ans, r - l + 1);
}
}
cout << ans << endl;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t = 1;
// cin >> t;
for(int T = 1; T <= t; T++) {
solve();
}
}
