#include <bits/stdc++.h>
using namespace std;
using ii = pair<int, int>;
using ll = long long;
#define mp make_pair
#define pb push_back
#define eb emplace_back
int N, K, H[605], C[605];
ll dp[605][305][305];
ii min_C[605], pref_min_C[605];
vector<int> vec[605];
vector<ll> arr[605];
vector<tuple<int, int, ll*> > queries[605];
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> N >> K;
for (int i = 0; i <= 600; i++) {
pref_min_C[i] = min_C[i] = mp((int)2e9, -1);
}
for (int i = 1; i <= N; i++) {
cin >> H[i] >> C[i];
vec[H[i]].pb(C[i]);
min_C[H[i]] = min(min_C[H[i]], mp(C[i], i));
}
pref_min_C[0] = min_C[0];
for (int i = 1; i <= 600; i++) {
pref_min_C[i] = min(min_C[i], pref_min_C[i - 1]);
}
for (int h_val = 601; h_val >= 0; h_val--) {
int min_C_idx = (h_val ? pref_min_C[h_val - 1].second : -1);
for (int v = 0; v <= 2 * N; v++) {
queries[v].clear();
}
for (int max_occ = 0; max_occ <= N; max_occ++) {
for (int carry = 0; carry <= N; carry++) {
if (h_val == 601) {
dp[h_val][max_occ][carry] = (carry ? (ll)1e18 : 0);
continue;
}
ll ret = (ll)1e18;
int cur_amt = vec[h_val].size() + carry;
if (cur_amt <= max_occ) {
dp[h_val][max_occ][carry] = dp[h_val + 1][max_occ][0];
} else if (min_C_idx == -1 || max_occ == 0) {
for (int x : {0, 1}) {
if (cur_amt - x > N) {
continue;
}
ret = min(ret, dp[h_val + 1][x][cur_amt - x] - (ll)x * K);
}
dp[h_val][max_occ][carry] = ret + (ll)cur_amt * K;
} else {
int l = max(cur_amt - N, max_occ), r = min(N, cur_amt);
for (int x = l; x <= r; x++) {
ret = min(ret, dp[h_val + 1][x][cur_amt - x] + (ll)x * (C[min_C_idx] - K));
}
dp[h_val][max_occ][carry] = (ll)cur_amt * K - (ll)max_occ * C[min_C_idx];
if (l <= r) {
queries[cur_amt].eb(l, r, &dp[h_val][max_occ][carry]);
}
}
}
}
if (h_val == 601 || min_C_idx == -1) {
continue;
}
for (int v = 0; v <= 2 * N; v++) {
arr[v].clear();
}
for (int max_occ = 0; max_occ <= N; max_occ++) {
for (int carry = 0; carry <= N; carry++) {
arr[max_occ + carry].pb(dp[h_val + 1][max_occ][carry] + (ll)max_occ * (C[min_C_idx] - K));
}
}
for (int v = 0; v <= 2 * N; v++) {
deque<int> Q;
int idx = 0;
for (auto [l, r, pos] : queries[v]) {
while (idx <= r) {
while (!Q.empty() && arr[v][Q.back()] >= arr[v][idx]) {
Q.pop_back();
}
Q.pb(idx);
idx++;
}
while (Q.front() < l) {
Q.pop_front();
}
*pos += arr[v][Q.front()];
}
}
}
cout << dp[0][0][0] << '\n';
}
