#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <vector>
#define endl '\n'
#define IOS                  \
    ios::sync_with_stdio(0); \
    cin.tie(0);              \
    cout.tie(0);
#define P pair<int, int>
#define endl '\n'
using namespace std;

typedef long long ll;
const int maxn = 500 * 2 + 10;
const ll inf = 1e18;
int n1, n2, cnt_edge = 1, S, T;
int head[maxn];
ll dis[maxn];
bool vis[maxn];
struct edge {
    int to, nxt;
    ll flow, cost;
} e[(maxn * maxn) << 2];
inline void add(int u, int v, ll w, ll c) {
    e[++cnt_edge].nxt = head[u];
    head[u] = cnt_edge;
    e[cnt_edge].to = v;
    e[cnt_edge].flow = w;
    e[cnt_edge].cost = c;
}
inline void addflow(int u, int v, ll w, ll c) {
    add(u, v, w, c);
    add(v, u, 0, -c);
}
inline bool spfa(int on) {
    memset(vis, 0, sizeof(vis));
    if (on == 1)
        for (int i = 0; i <= T; i++) dis[i] = inf;
    else
        for (int i = 0; i <= T; i++) dis[i] = -inf;

    queue<int> q;
    q.push(S);
    dis[S] = 0;
    vis[S] = 1;
    while (!q.empty()) {
        int x = q.front();
        q.pop();
        vis[x] = 0;
        for (int i = head[x]; i; i = e[i].nxt) {
            int y = e[i].to;
            // cout << "->" << y << endl;
            if ((on == 1 && e[i].flow && dis[y] > dis[x] + e[i].cost) ||
                (on == -1 && e[i].flow && dis[y] < dis[x] + e[i].cost)) {
                dis[y] = dis[x] + e[i].cost;
                if (!vis[y]) q.push(y), vis[y] = 1;
            }
        }
    }
    if (on == 1)
        return dis[T] != inf;
    else
        return dis[T] != -inf;
}
ll dfs(int x, ll lim) {
    vis[x] = 1;
    if (x == T || lim <= 0) return lim;
    ll res = lim;
    for (int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if (dis[y] != dis[x] + e[i].cost || e[i].flow <= 0 || vis[y]) continue;
        ll tmp = dfs(y, min(res, e[i].flow));
        res -= tmp;
        e[i].flow -= tmp;
        e[i ^ 1].flow += tmp;
        if (res <= 0) break;
    }
    return lim - res;
}
inline ll Dinic(int on) {
    ll res = 0, cost = 0;
    while (spfa(on)) {
        ll flow = dfs(S, inf);
        res += flow, cost += flow * dis[T];
    }
    return cost;
}
int id(int x, int y, int in) {
    return 2 * ((n1 * 2 + x - 2) * (x - 1) / 2 + y - 1) + in;
}

int nn, k;
int l[maxn], r[maxn], a[maxn];
int main() {
    cin >> nn >> k;
    for (int i = 1; i <= nn; i++) {
        cin >> l[i] >> r[i];
        if (l[i] > r[i]) swap(l[i], r[i]);
        a[i] = l[i], a[i + nn] = r[i];
    }
    sort(a + 1, a + nn * 2 + 1);
    int n = unique(a + 1, 1 + a + nn * 2) - a-1;
    S = n + 1, T = S + 1;
    for (int i = 1; i <= nn; i++) {
        int L = lower_bound(a + 1, a + 1 + n, l[i]) - a;
        int R = lower_bound(a + 1, a + 1 + n, r[i]) - a;
        addflow(L, R, 1, r[i] - l[i]);
    }

    for (int i = 1; i < n; i++) {
        addflow(i, i + 1, inf, 0);
    }
    addflow(S, 1, k, 0);
    addflow(n, T, k, 0);
    // cout << "build c\n";
    cout << Dinic(-1);
    return 0;
}