// He was a moth to the flame
// She was holding the matches
// Soon, she's gonna find stealing other people's toys
// On the playground won't make you many friends
#include <algorithm>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <vector>
typedef long long ll;
typedef long double ld;
using namespace std;
const ll inf = 1e18;
const int maxn = 301;
// dp[vyska v ktorej som][pocet zadarmo hran][pocet tych, co prisli na tuto vysku zdola] = minimalna cena
ll dp[2][maxn][maxn];
void clear(int i)
{
for (int a = 0; a < maxn; a++) for (int b = 0; b < maxn; b++) for (int c = 0; c < maxn; c++)
dp[i][a][b] = inf;
}
void upd(ll& a, ll b)
{
a = min(a, b);
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n;
ll k;
cin >> n >> k;
vector<int> hi(n), ci(n);
vector<ll> cs, hs;
for (int i = 0; i < n; i++) cin >> hi[i] >> ci[i], cs.push_back(ci[i]), hs.push_back(hi[i]), hs.push_back(hi[i] + 1);
cs.push_back(inf);
sort(cs.begin(), cs.end());
hs.push_back(1e9 + 500);
sort(hs.begin(), hs.end());
hs.erase(unique(hs.begin(), hs.end()), hs.end());
for (int i = 0; i < n; i++) ci[i] = lower_bound(cs.begin(), cs.end(), ci[i]) - cs.begin(), hi[i] = lower_bound(hs.begin(), hs.end(), hi[i]) - hs.begin();
int h = hs.size();
vector<int> cnth(h);
vector<int> minc(h, n);
for (int i = 0; i < n; i++) cnth[hi[i]]++, minc[hi[i]] = min(minc[hi[i]], ci[i]);
vector<vector<ll> > cnt(n + 1, vector<ll>(n + 1, 0));
for (ll z = 1; z <= n; z++) for (ll up = 1; up <= n; up++)
{
if (up % z == 0) cnt[z][up] = cnt[z][up - z] + z * k * (up / z);
else cnt[z][up] = cnt[z][up - (up % z)] + (up % z) * k * (up / z + 1);
}
ll ans = inf;
clear(0);
int c = minc[0];
dp[0][1][cnth[0] - 1] = 0;
for (int h2 = 0; h2 + 1 < h; h2++) // robime prechody na ten o jeden viac
{
int pv = h2 & 1, nw = (h2 + 1) & 1;
clear(nw);
for (int z = 0; z <= n; z++) for (int up = 0; up <= n; up++) if (dp[pv][z][up] != inf)
{
int total = up + cnth[h2 + 1];
if (!total)
{
upd(dp[nw][z][total], dp[pv][z][up]);
continue;
}
ll val = dp[pv][z][up];
ll rmv = min((ll)up, (hs[h2 + 1] - hs[h2] - 1) * z);
val += cnt[z][rmv];
val += ((ll)(up - rmv)) * k * (hs[h2 + 1] - hs[h2]);
for (int stay = 0; stay <= total - rmv; stay++) // pocet tych co tu ostanu
{
int z2 = max(stay, z);
int up2 = total - stay - rmv;
ll cena = val + max(0ll, (ll)(stay - z)) * 1ll * cs[c];
upd(dp[nw][z2][up2], cena);
}
}
c = min(c, minc[h2 + 1]);
}
for (int z = 0; z <= n; z++) upd(ans, dp[(h - 1) & 1][z][0]);
cout << ans << "\n";
return 0;
}
