#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define vc vector
#define st first
#define nd second
#define all(a) a.begin(), a.end()
#define sz(a) (ll)a.size()
#define pub push_back
#define pob pop_back
ll INF = 1e18;
struct P {
ll h, c;
};
ll n, X;
vc<P> a;
void input() {
cin >> n >> X;
a.resize(n);
for (ll i = 0; i < n; i++)
cin >> a[i].h >> a[i].c;
}
void solve() {
if (n == 1) {
cout << "0\n";
return;
}
sort(all(a), [](auto &p, auto &q) {
if (p.h != q.h)
return p.h < q.h;
return p.c < q.c;
});
ll ans = 0;
for (ll i = 1; i < n; i++)
if (a[i].h == a[0].h) {
ans += X;
a[i].h++;
}
sort(all(a), [](auto &p, auto &q) {
if (p.h != q.h)
return p.h < q.h;
return p.c < q.c;
});
ll H = 0;
for (ll i = 0; i < n; i++)
H = max(H, a[i].h);
vc<vc<vc<vc<ll>>>> dp(n + H + 1, vc<vc<vc<ll>>>(n, vc<vc<ll>>(n, vc<ll>(n, INF))));
dp[a[0].h][1][0][0] = 0;
for (ll h = a[0].h; h < n + H; h++)
for (ll v = 0; v < n; v++)
for (ll c = 0; c < n; c++)
for (ll i = 0; i < n; i++) {
if (dp[h][v][c][i] == INF)
continue;
ll l = 0;
while (l < n and a[l].h <= h)
l++;
ll r = l - 1;
pll mn = {a[i].c, i};
while (r + 1 < n and a[r + 1].h == h + 1)
r++;
ll s = r - l + 1;
for (ll f = 0; f <= s + c; f++) {
ll h1 = h + 1;
ll v1 = max(0ll, v - f) + f;
ll c1 = s + c - f;
ll i1 = mn.nd;
ll x = dp[h][v][c][i];
x += max(0ll, f - v) * a[i].c;
x += c1 * X;
dp[h1][v1][c1][i1] = min(dp[h1][v1][c1][i1], x);
if (l + f <= r)
mn = min(mn, {a[l + f].c, l + f});
}
}
ll mndp = INF;
for (ll v = 0; v < n; v++)
for (ll i = 0; i < n; i++)
mndp = min(mndp, dp[n + H][v][0][i]);
cout << mndp + ans << "\n";
}
void program() {
input();
solve();
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
program();
return 0;
}
