#include <bits/stdc++.h>
#include <atcoder/modint>
using namespace atcoder;
//#pragma GCC optimize ("O3")
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()

using ll = long long;
using vec = vector<ll>;
using mat = vector<vec>;

ll N,M,H,W,Q,K,A,B;
string S;
using P = pair<ll, ll>;
using tp = tuple<ll, ll, ll>;
const ll INF = (1LL<<60);

template<class T> bool chmin(T &a, const T b){
    if(a > b) {a = b; return true;}
    else return false;
}
template<class T> bool chmax(T &a, const T b){
    if(a < b) {a = b; return true;}
    else return false;
}
template<class T> void my_printv(std::vector<T> v,bool endline = true){
    if(!v.empty()){
        for(std::size_t i{}; i<v.size()-1; ++i) std::cout<<v[i]<<" ";
        std::cout<<v.back();
    }
    if(endline) std::cout<<std::endl;
}

using mint = modint998244353;
using vm = vector<mint>;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin>>N>>K;
    vec p(N), q(N);
    rep(i, N) cin>>p[i]>>q[i];
    const int st = (int)1e+8;
    auto ok = [&](int bd){
        vec dp(N);
        rep(i, N){
            if(st - p[i] < bd){
                dp[i] = - INF;
            }else{
                dp[i] = st - p[i];
            }
        }
        rep(lp, K - 1){
            vec ndp(N, -INF);
            rep(lp2, 2) {
                M = -INF;
                rep(tmp, N) {
                    int i = (lp2 ? N - 1 - tmp : tmp);
                    chmax(ndp[i], M);
                    if (dp[i] - p[i] >= bd) chmax(M, dp[i] + q[i] - p[i]);
                }
            }
            dp = ndp;
        }
        return *max_element(ALL(dp)) != -INF;
    };
    ll lb = 0, ub = st * 2;
    while(ub - lb > 1){
        ll cen = lb + (ub - lb) / 2;
        (ok(cen) ? lb : ub) = cen;
    }
    cout<<lb - st<<endl;
}