//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#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 mxn=305;
vector<vector<ll>> dp(mxn,vector<ll>(mxn,inf));
int 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> cnt(2*mxn);
vector<ll> mn(2*mxn,inf);
for(int i=0;i<n;i++){
cnt[h[i]]++;
mn[h[i]]=min(mn[h[i]],c[i]);
}
ll curmn=mn[mnh];
dp[1][0]=0;
for(int i=mnh+1;i<2*mxn;i++){
vector<vector<ll>> dpn(mxn,vector<ll>(mxn,inf));
for(int j=0;j<=n;j++){
for(int k=0;k<=n;k++){
dpn[j][max(0,k+cnt[i]-j)]=min(dpn[j][max(0,k+cnt[i]-j)],dp[j][k]+K*k);
}
}
for(int j=0;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
