#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 301;
const ll inf = 1e18;
inline void upd(ll & x, ll y) {
if (x > y) x = y;
}
ll dp[N][N];
ll ndp[N][N];
void reset() {
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
ndp[i][j] = inf;
}
}
}
void fini() {
for (int i = 0; i < N; ++i) {
for (int j = N - 1; j >= 0; --j) {
dp[i][j] = ndp[i][j];
// if (i) upd(dp[i][j], dp[i - 1][j]);
// if (j + 1 < N) upd(dp[i][j], dp[i][j + 1]);
}
}
}
void copy() {
for (int i = 0; i < N; ++i) {
for (int j = N - 1; j >= 0; --j) {
ndp[i][j] = dp[i][j];
}
}
}
void print() {
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
cout << (dp[i][j] == inf ? -1 : dp[i][j]) << " \n"[j + 1 == N];
}
}
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
dp[i][j] = ndp[i][j] = inf;
}
}
int n;
ll k;
cin >> n >> k;
vector<pair<int, int>> a(n);
vector<int> v;
for (auto & [x, y]: a) { // height, cost
cin >> x >> y;
v.push_back(x);
}
if (n == 1) {
cout << 0 << '\n';
exit(0);
}
sort(v.begin(), v.end());
for (int i = 1; i < n; ++i) {
while (v[i] <= v[i - 1]) v[i]++;
}
vector<int> cnt(n, 0);
vector<ll> cost(n, inf);
for (auto [x, y]: a) {
for (int i = 0; i < n; ++i) {
if (v[i] == x) {
cnt[i]++;
upd(cost[i], y);
}
}
}
// manually compute dp for first thing
dp[0][1] = k * (cnt[0] - 1);
cnt[1] += cnt[0] - 1;
ll best = cost[0];
for (int i = 1; i < n; ++i) {
// cout << cnt[i] << "\n";
if (cnt[i]) {
reset();
for (int x = 0; x <= n; ++x) {
for (int y = 0; y <= n; ++y) {
if (x + cnt[i] <= n) {
upd(ndp[x + cnt[i]][y], dp[x][y]);
}
}
}
fini();
}
// cout << "WTf\n";
// print();
reset();
for (int x = 0; x <= n; ++x) {
for (int y = 0; y <= n; ++y) { // go to next
if (dp[x][y] == inf) continue;
for (int z = 0;; ++z) {
// if (x - y - z < 0 || y + z > n) break;
if (y + z > n) break;
if (x - y < 0 && z) break;
upd(ndp[max(0LL, (ll)x - y - z)][y + z], dp[x][y] + best * z + k * max(0LL, (ll)x - y - z));
}
}
}
fini();
best = min(best, cost[i]);
// cout << "? " << best << " " << i << '\n';
// print();
}
ll ans = inf;
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
if (i == 0) ans = min(ans, dp[i][j]);
}
}
cout << ans << '\n';
}
