#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;
ll ans = INF;
vc<ll> par = {-1};
void input() {
cin >> n >> X;
a.resize(n);
for (ll i = 0; i < n; i++)
cin >> a[i].h >> a[i].c;
}
void rec(ll i = 1) {
if (i == n) {
ll x = 0;
vc<ll> h(n), d(n, -1);
h[0] = a[0].h;
for (ll j = 1; j < n; j++)
d[par[j]]++;
for (ll j = 1; j < n; j++)
for (ll k = 1; k < n; k++)
h[k] = max(max(h[k], a[k].h), h[par[k]] + 1);
for (ll j = 0; j < n; j++) {
x += max(0ll, d[j]) * a[j].c;
x += (h[j] - a[j].h) * X;
}
ans = min(ans, x);
return;
}
for (ll p = 0; p < n; p++) {
if (p == i)
continue;
par.pub(p);
rec(i + 1);
par.pob();
}
}
void solve() {
sort(all(a), [](auto &p, auto &q) {
if (p.h != q.h)
return p.h < q.h;
return p.c < q.c;
});
rec();
cout << ans << "\n";
}
void program() {
input();
solve();
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
program();
return 0;
}
