/*************************************
* author: marvinthang *
* created: 21.03.2024 17:10:36 *
*************************************/
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define left ___left
#define right ___right
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
#define MASK(i) (1LL << (i))
#define BIT(x, i) ((x) >> (i) & 1)
#define __builtin_popcount __builtin_popcountll
#define ALL(v) (v).begin(), (v).end()
#define REP(i, n) for (int i = 0, _n = (n); i < _n; ++i)
#define REPD(i, n) for (int i = (n); i-- > 0; )
#define FOR(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define FORD(i, b, a) for (int i = (b), _a = (a); --i >= _a; )
#define FORE(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORDE(i, b, a) for (int i = (b), _a = (a); i >= _a; --i)
#define scan_op(...) istream & operator >> (istream &in, __VA_ARGS__ &u)
#define print_op(...) ostream & operator << (ostream &out, const __VA_ARGS__ &u)
#ifdef LOCAL
#include "debug.h"
#else
#define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
#define DB(...) 23
#define db(...) 23
#define debug(...) 23
#endif
template <class U, class V> scan_op(pair <U, V>) { return in >> u.first >> u.second; }
template <class T> scan_op(vector <T>) { for (size_t i = 0; i < u.size(); ++i) in >> u[i]; return in; }
template <class U, class V> print_op(pair <U, V>) { return out << '(' << u.first << ", " << u.second << ')'; }
template <size_t i, class T> ostream & print_tuple_utils(ostream &out, const T &tup) { if constexpr(i == tuple_size<T>::value) return out << ")"; else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); }
template <class ...U> print_op(tuple<U...>) { return print_tuple_utils<0, tuple<U...>>(out, u); }
template <class Con, class = decltype(begin(declval<Con>()))> typename enable_if <!is_same<Con, string>::value, ostream&>::type operator << (ostream &out, const Con &con) { out << '{'; for (__typeof(con.begin()) it = con.begin(); it != con.end(); ++it) out << (it == con.begin() ? "" : ", ") << *it; return out << '}'; }
template <class A, class B> bool minimize(A &a, B b) { return a > b ? a = b, true : false; }
template <class A, class B> bool maximize(A &a, B b) { return a < b ? a = b, true : false; }
// end of template
const int MAX_H = 2e9 + 7;
const long long INF = 1e18;
void process(void) {
int N, K; cin >> N >> K;
vector <pair <int, int>> points(N); cin >> points;
if (N == 1) return void(cout << "0\n");
sort(ALL(points));
long long add = 0;
FOR(i, 1, N) {
if (points[i].fi == points[0].fi) {
++points[i].fi;
add += K;
}
}
sort(ALL(points), [&] (pair <int, int> x, pair <int, int> y) { return pair{x.fi, y.se} < pair{y.fi, x.se}; });
points.emplace_back(MAX_H - 2, 0);
++N;
int last = 0;
vector dp(N, vector<long long>(N, INF));
dp[1][0] = 0;
map <int, int> cnt;
vector <long long> min_pref(N, INF);
FOR(p, 1, N) if ((p == N - 1 || points[p].fi != points[p + 1].fi) && points[p].se < points[last].se) {
vector nxt_dp(N, vector<long long>(N, INF));
REP(f, max(last + 1, 2)) {
FORE(c, 1, max(p, 1)) min_pref[c] = min(min_pref[c - 1], dp[c][f] - 1LL * c * points[last].se);
cnt.clear();
FORE(i, last + 1, p) cnt[points[i].fi]++;
cnt[points[last].fi + 1] += f;
long long cur = 0;
FORDE(c, max(p, 1), 1) {
for (auto &[h, x]: cnt) {
if (h > points[p].fi) break;
if (x > c) {
cnt[h + 1] += x - c;
cur += 1LL * (x - c) * K;
x = c;
}
}
minimize(nxt_dp[c][cnt[points[p].fi + 1]], 1LL * c * points[last].se + cur + min_pref[c]);
}
}
last = p;
dp.swap(nxt_dp);
}
long long res = INF;
REP(i, N) REP(j, N) minimize(res, dp[i][j]);
cout << res + add << '\n';
}
int main(void) {
ios_base::sync_with_stdio(false); cin.tie(nullptr); // cout.tie(nullptr);
file("ski2");
// int t; cin >> t; while (t--)
process();
// cerr << "Time elapsed: " << TIME << " s.\n";
return (0^0);
}
