#include <bits/stdc++.h>
#define rep(i,a,b) for(int i = (a); i <= (b); i++)
#define rng(a) a.begin(), a.end()
#define ina(n,a) cin >> n; for(int i = 1; i <= n; i++) cin >> a[i]
#define sz(x) (int)(x).size()
#define se second
#define fi first
#define prev            coyhhhhhhyoc    
#define next          sdNNNmNNNNNNNmds  
#define y0           hNNNNy_yNNNNNN_sNh
#define y1          mNNNNNdtdNNNNNNtsNNm
#define yn          mNNNNNNNNy___smNNNms
#define tm            oooooosyysooooot 
#define read               tyhyt        
#define rank              ytmNmo         
#define index              yyy
#define pb push_back
#define pcnt __builtin_popcountll
#define rrep(i,a,b) for(int i = (b); i >= (a); i--)
#define rall(x,a) for(auto x : a)
#define MOD 1000000007
#define endl "\n"
typedef long long ll;
using namespace std;

struct Dish {
    int p, q;
};

bool operator < (const Dish& d, const Dish& e) {
    int diff = d.q - d.p;
    int difff = e.q - e.p;
    return diff > difff;
}

const int N = 1111;
Dish ds[N];
int n, d;

int solve() {
    cin >> n >> d;
    rep(i, 1, n) {
        cin >> ds[i].p >> ds[i].q;
    }
    sort(ds + 1, ds + n + 1);
    int ans = 0, en = 0, pr = 0;
    rep(i, 1, d) {
        int cur = pr == 1 ? 2 : 1;
        en -= ds[cur].p;
        ans = min(ans, en);
        en += ds[cur].q;
        pr = cur;
    }
    cout << ans << endl;
    return 0;
}
 
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    while(t--) {
        solve();
    }
    return 0;
}