//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define int ll
#define pii pair<int,int>
#define f first
#define s second
#define all(x) x.begin(),x.end()
#define _ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int dx[4]={0,0,1,-1};
int dy[4]={1,-1,0,0};
void setIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
const ll inf=(ll)1e18;
const int inf2=2e9;
const int mxn=305;
vector<vector<ll>> dp(mxn,vector<ll>(mxn,inf));
signed main() {_
ll n,K;
cin>>n>>K;
vector<ll> h(n),c(n);
for(int i=0;i<n;i++){
cin>>h[i]>>c[i];
}
ll mnh=*min_element(all(h));
ll mnc=inf;
for(int i=0;i<n;i++){
if(h[i]==mnh) mnc=min(mnc,c[i]);
}
int pos;
for(int i=0;i<n;i++){
if(h[i]==mnh and c[i]==mnc){
pos=i;
break;
}
}
ll sum=0;
for(int i=0;i<n;i++){
if(h[i]==mnh and i!=pos){
h[i]++;
sum+=K;
}
}
vector<int> xs;
for(int i=0;i<n;i++){
xs.push_back(h[i]);
xs.push_back(h[i]+1);
}
xs.push_back(inf2);
sort(all(xs));
xs.resize(unique(all(xs))-xs.begin());
int sz=(int)xs.size();
vector<int> cnt(sz);
vector<ll> mn(sz,inf);
for(int i=0;i<n;i++){
int pos=lower_bound(all(xs),h[i])-xs.begin();
cnt[pos]++;
mn[pos]=min(mn[pos],c[i]);
}
auto cost=[&](int k,int j,int d){
int dd=min(d,k/j);
ll ans=1ll*(dd)*(dd+1)/2*j*K;
int r=k-dd*j;
ans+=1ll*r*(dd+1)*K;
//cout<<k<<' '<<j<<' '<<d<<' '<<ans<<'\n';
return ans;
};
ll curmn=mn[0];
dp[1][0]=0;
for(int i=1;i<sz;i++){
vector<vector<ll>> dpn(mxn,vector<ll>(mxn,inf));
int d=xs[i]-xs[i-1]-1;
for(int j=1;j<=n;j++){
for(int k=0;k<=n;k++){
dpn[j][max(0ll,max(0ll,k-j*d)+cnt[i]-j)]=min(dpn[j][max(0ll,max(0ll,k-j*d)+cnt[i]-j)],dp[j][k]+cost(k,j,d));
}
}
for(int j=1;j<=n;j++){
for(int k=0;k<=n;k++){
if(k>0) dpn[j+1][k-1]=min(dpn[j+1][k-1],dpn[j][k]+curmn);
}
}
swap(dp,dpn);
curmn=min(curmn,mn[i]);
}
ll ans=inf;
for(int j=0;j<=n;j++){
ans=min(ans,dp[j][0]);
}
cout<<ans+sum<<'\n';
return 0;
}
//maybe its multiset not set
//yeeorz
//diaoborz
// dp(i,j,k)->dp(i,j+1,k-1)+mn
// dp(i,j,k)->dp(i+1,j,max(0,k+cnt[i+1]-j))+K*k
