费用流，离散化后，l向r连费用为负长度的边容量为1
相邻的连容量为k的边，最好建S和T
# include <bits/stdc++.h>
# define RG register
# define IL inline
# define Fill(a, b) memset(a, b, sizeof(a))
# define Copy(a, b) memcpy(a, b, sizeof(a))
using namespace std;
typedef long long ll;
const int _(1010), __(1e6 + 10), INF(2e9);
IL ll Read(){
char c = '%'; ll x = 0, z = 1;
for(; c > '9' || c < '0'; c = getchar()) if(c == '-') z = -1;
for(; c >= '0' && c <= '9'; c = getchar()) x = x * 10 + c - '0';
return x * z;
}
int n, k, l[_], r[_], o[_], len;
int cnt, fst[_], w[__], to[__], nxt[__], dis[_], vis[_], S, T, cost[__], pe[_], pv[_], max_flow, max_cost;
queue <int> Q;
IL void Add(RG int u, RG int v, RG int f, RG int co){
cost[cnt] = co; w[cnt] = f; to[cnt] = v; nxt[cnt] = fst[u]; fst[u] = cnt++;
cost[cnt] = -co; w[cnt] = 0; to[cnt] = u; nxt[cnt] = fst[v]; fst[v] = cnt++;
}
IL bool Bfs(){
Q.push(S); Fill(dis, 127); dis[S] = 0; vis[S] = 1;
while(!Q.empty()){
RG int u = Q.front(); Q.pop();
for(RG int e = fst[u]; e != -1; e = nxt[e]){
if(!w[e] || dis[to[e]] <= dis[u] + cost[e]) continue;
dis[to[e]] = dis[u] + cost[e];
pe[to[e]] = e; pv[to[e]] = u;
if(!vis[to[e]]) vis[to[e]] = 1, Q.push(to[e]);
}
vis[u] = 0;
}
if(dis[T] >= dis[T + 1]) return 0;
RG int ret = INF;
for(RG int u = T; u != S; u = pv[u]) ret = min(ret, w[pe[u]]);
for(RG int u = T; u != S; u = pv[u]) w[pe[u]] -= ret, w[pe[u] ^ 1] += ret;
max_cost -= ret * dis[T]; max_flow += ret;
return 1;
}
int main(RG int argc, RG char *argv[]){
Fill(fst, -1); n = Read(); k = Read();
for(RG int i = 1; i <= n; ++i){
l[i] = Read(); r[i] = Read();
o[++cnt] = l[i]; o[++cnt] = r[i];
}
sort(o + 1, o + cnt + 1); len = unique(o + 1, o + cnt + 1) - o - 1;
cnt = 0; T = len + 1;
for(RG int i = 0; i <= len; ++i) Add(i, i + 1, k, 0);
for(RG int i = 1; i <= n; ++i){
if(l[i] >= r[i]) continue;
RG int le = r[i] - l[i];
l[i] = lower_bound(o + 1, o + len + 1, l[i]) - o;
r[i] = lower_bound(o + 1, o + len + 1, r[i]) - o;
Add(l[i], r[i], 1, -le);
}
while(Bfs()); printf("%d\n", max_cost);
return 0;
}