#include<bits/stdc++.h>
using namespace std;
#define int long long
mt19937 rng(69420);
int rand(int l, int r){
return uniform_int_distribution<int>(l, r)(rng);
}
double rand_double(int l, int r){
return uniform_real_distribution<double>(l, r)(rng);
}
const int N=310, inf=LLONG_MAX;
int n, k, h[N], c[N];
struct State{
int add[N];
int value;
void init_random(){
for (int i=1; i<=n; ++i) add[i]=rand(0, n);
}
void evaluate(){
value=accumulate(add+1, add+n+1, 0ll)*k;
vector<pair<int, int>> v;
for (int i=1; i<=n; ++i) v.emplace_back(h[i]+add[i], i);
sort(v.begin(), v.end());
if (v[0].first==v[1].first){
value=inf;
return;
}
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq;
pq.emplace(0, v[0].second);
for (int i=1; i<n; ++i){
int j=i;
while (j+1<n && v[j+1].first==v[i].first) ++j;
for (int l=i; l<=j; ++l){
value+=pq.top().first;
if (pq.top().first==0){
int id=pq.top().second; pq.pop();
pq.emplace(c[id], id);
}
}
for (int l=i; l<=j; ++l) pq.emplace(0, v[l].second);
i=j;
}
}
State (){
memset(add, 0, sizeof add);
value=0;
}
};
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> k;
if (n==1){
cout << 0;
return 0;
}
for (int i=1; i<=n; ++i) cin >> h[i] >> c[i];
auto time=clock();
State state, best;
best.evaluate();
int ans=inf;
double temp=1e5;
state.init_random(); state.evaluate();
while ((clock()-time)*1000/CLOCKS_PER_SEC<1900){
int i=rand(1, n);
int j=0;
if (state.add[i]==0) j=1;
else if (state.add[i]==n) j=-1;
else j=rand(0, 1), j-=!j;
int old_score=state.value;
state.add[i]+=j; state.evaluate();
int new_score=state.value;
ans=min(ans, new_score);
if (new_score<old_score);
else if (exp((old_score-new_score)/temp)>rand_double(0, 1));
else state.add[i]-=j, state.value=old_score;
temp*=0.999;
}
cout << ans;
return 0;
}
