#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define pb(...) emplace_back(__VA_ARGS__)
#define mp(a, b) make_pair(a, b)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define lscan(x) scanf("%I64d", &x)
#define lprint(x) printf("%I64d", x)
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define rep2(i, n) for (ll i = (ll)n - 1; i >= 0; i--)
#define REP(i, l, r) for (ll i = l; i < (r); i++)
#define REP2(i, l, r) for (ll i = (ll)r - 1; i >= (l); i--)
#define siz(x) (ll) x.size()
template <class T>
using rque = priority_queue<T, vector<T>, greater<T>>;

template <class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}

template <class T>
bool chmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return 1;
    }
    return 0;
}

ll gcd(ll a, ll b) {
    if (a == 0)
        return b;
    if (b == 0)
        return a;
    ll cnt = a % b;
    while (cnt != 0) {
        a = b;
        b = cnt;
        cnt = a % b;
    }
    return b;
}

long long extGCD(long long a, long long b, long long &x, long long &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

struct UnionFind {
    vector<ll> data;
    int num;

    UnionFind(int sz) {
        data.assign(sz, -1);
        num = sz;
    }

    bool unite(int x, int y) {
        x = find(x), y = find(y);
        if (x == y)
            return (false);
        if (data[x] > data[y])
            swap(x, y);
        data[x] += data[y];
        data[y] = x;
        num--;
        return (true);
    }

    int find(int k) {
        if (data[k] < 0)
            return (k);
        return (data[k] = find(data[k]));
    }

    ll size(int k) {
        return (-data[find(k)]);
    }

    bool same(int x, int y) {
        return find(x) == find(y);
    }
};

template <int mod>
struct ModInt {
    int x;

    ModInt() : x(0) {
    }

    ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {
    }

    ModInt &operator+=(const ModInt &p) {
        if ((x += p.x) >= mod)
            x -= mod;
        return *this;
    }

    ModInt &operator-=(const ModInt &p) {
        if ((x += mod - p.x) >= mod)
            x -= mod;
        return *this;
    }

    ModInt &operator*=(const ModInt &p) {
        x = (int)(1LL * x * p.x % mod);
        return *this;
    }

    ModInt &operator/=(const ModInt &p) {
        *this *= p.inverse();
        return *this;
    }

    ModInt operator-() const {
        return ModInt(-x);
    }

    ModInt operator+(const ModInt &p) const {
        return ModInt(*this) += p;
    }

    ModInt operator-(const ModInt &p) const {
        return ModInt(*this) -= p;
    }

    ModInt &operator++() {
        return *this += ModInt(1);
    }

    ModInt operator++(int) {
        ModInt tmp = *this;
        ++*this;
        return tmp;
    }

    ModInt &operator--() {
        return *this -= ModInt(1);
    }

    ModInt operator--(int) {
        ModInt tmp = *this;
        --*this;
        return tmp;
    }

    ModInt operator*(const ModInt &p) const {
        return ModInt(*this) *= p;
    }

    ModInt operator/(const ModInt &p) const {
        return ModInt(*this) /= p;
    }

    bool operator==(const ModInt &p) const {
        return x == p.x;
    }

    bool operator!=(const ModInt &p) const {
        return x != p.x;
    }

    ModInt inverse() const {
        int a = x, b = mod, u = 1, v = 0, t;
        while (b > 0) {
            t = a / b;
            swap(a -= t * b, b);
            swap(u -= t * v, v);
        }
        return ModInt(u);
    }

    ModInt pow(int64_t n) const {
        ModInt ret(1), mul(x);
        while (n > 0) {
            if (n & 1)
                ret *= mul;
            mul *= mul;
            n >>= 1;
        }
        return ret;
    }

    friend ostream &operator<<(ostream &os, const ModInt &p) {
        return os << p.x;
    }

    friend istream &operator>>(istream &is, ModInt &a) {
        int64_t t;
        is >> t;
        a = ModInt<mod>(t);
        return (is);
    }

    static int get_mod() {
        return mod;
    }
};

ll mpow2(ll x, ll n, ll mod) {
    ll ans = 1;
    while (n != 0) {
        if (n & 1)
            ans = ans * x % mod;
        x = x * x % mod;
        n = n >> 1;
    }
    return ans;
}
ll modinv2(ll a, ll mod) {
    ll b = mod, u = 1, v = 0;
    while (b) {
        ll t = a / b;
        a -= t * b;
        swap(a, b);
        u -= t * v;
        swap(u, v);
    }
    u %= mod;
    if (u < 0)
        u += mod;
    return u;
}

constexpr int mod = 1000000007;
// constexpr int mod = 998244353;
// constexpr int mod = 31607;
using mint = ModInt<mod>;

mint mpow(mint x, ll n) {
    mint ans = 1;
    while (n != 0) {
        if (n & 1)
            ans *= x;
        x *= x;
        n = n >> 1;
    }
    return ans;
}

// ----- library -------
// ----- library -------

int main() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    cout << fixed << setprecision(15);

    ll n, d;
    cin >> n >> d;
    vector<ll> p(n), q(n + 1), r(n + 1);
    rep(i, n) cin >> p[i] >> q[i], r[i] = q[i] - p[i];
    q[n] = 1e9, r[n] = 1e9;
    vector<pair<ll, ll>> mq(100001, {n, n}), mr(100001, {n, n});
    rep(i, n) {
        if (q[mq[p[i]].second] > q[i])
            mq[p[i]].second = i;
        if (q[mq[p[i]].first] > q[mq[p[i]].second])
            swap(mq[p[i]].first, mq[p[i]].second);
        if (r[mr[p[i]].second] > r[i])
            mr[p[i]].second = i;
        if (r[mr[p[i]].first] > r[mr[p[i]].second])
            swap(mr[p[i]].first, mr[p[i]].second);
    }
    REP(i, 1, 100000) {
        if (q[mq[i].first] < q[mq[i + 1].second])
            mq[i + 1].second = mq[i].first;
        if (q[mq[i + 1].first] > q[mq[i + 1].second])
            swap(mq[i + 1].first, mq[i + 1].second);
        if (q[mq[i].second] < q[mq[i + 1].second])
            mq[i + 1].second = mq[i].second;
        if (r[mr[i].first] < r[mr[i + 1].second])
            mr[i + 1].second = mr[i].first;
        if (r[mr[i + 1].first] > r[mr[i + 1].second])
            swap(mr[i + 1].first, mr[i + 1].second);
        if (r[mr[i].second] < r[mr[i + 1].second])
            mr[i + 1].second = mr[i].second;
    }
    ll ok = -1e9, ng = 0;
    while (ng - ok > 1) {
        ll mid = (ok + ng) / 2;
        vector<ll> dp(n, 0), ndp(n);
        rep(t, d) {
            fill(all(ndp), -1e9);
            rep(i, n) {
                ll rest = max(min(dp[i] - mid, 100000ll), 0ll);
                ll idx = mq[rest].first;
                if (idx != n && idx != i)
                    chmax(ndp[idx], dp[i] + r[idx]);
                idx = mq[rest].second;
                if (idx != n && idx != i)
                    chmax(ndp[idx], dp[i] + r[idx]);
                idx = mr[rest].first;
                if (idx != n && idx != i)
                    chmax(ndp[idx], dp[i] + r[idx]);
                idx = mr[rest].second;
                if (idx != n && idx != i)
                    chmax(ndp[idx], dp[i] + r[idx]);
            }
            swap(dp, ndp);
        }
        int flag = 0;
        rep(i, n) if (dp[i] >= mid) flag = 1;
        if (flag)
            ok = mid;
        else
            ng = mid;
    }
    cout << ok << endl;
}