#include<bits/stdc++.h>
#define MAXN 107
using namespace std;
const long long inf=1e15;
struct tower{
int h,c;
inline friend bool operator < (tower fr,tower sc){
if(fr.h==sc.h)return fr.c<sc.c;
return fr.h<sc.h;
}
}a[MAXN];
int n,K;
long long dp[MAXN][MAXN][MAXN];
long long cost(int x,int y){
return (abs(a[x].h-a[y].h)+1)*K;
}
int main(){
cin>>n>>K;
for(int i=1;i<=n;i++){
cin>>a[i].h>>a[i].c;
}
sort(a+1,a+n+1);
a[0].h=-1;
for(int pos=n+1;pos>=1;pos--){
for(int last=0;last<pos;last++){
for(int taken=0;taken<=last;taken++){
if(pos==n+1 and last==0){
dp[pos][last][taken]=inf;
continue;
}
if(pos==n+1){
for(int i=last+1;i<=n;i++){
if(a[i].h==a[last].h)dp[pos][last][taken]+=K;
else break;
}
dp[pos][last][taken]+=max(n-last-1,0) * a[last].c;
if(taken>0 and last==n)dp[pos][last][taken]-=a[last].c;
continue;
}
dp[pos][last][taken]=dp[pos+1][last][taken];
if(a[pos].h==a[last].h)continue;
long long sum=0,take=0;
for(int i=last+1;i<pos;i++){
if(last!=0 and a[last].c+(a[i].h==a[last].h)*K<=a[pos].c+cost(i,pos)){
sum+=a[last].c+(a[i].h==a[last].h)*K;
}else{
take++;
sum+=cost(i,pos) + a[pos].c;
}
}
if(last==0 or a[last].c>a[pos].c + cost(last,pos)){
take+=taken;
sum+=-(taken)*a[last].c + taken*(a[pos].c + cost(last,pos));
}
dp[pos][last][taken]=min(dp[pos][last][taken] , dp[pos+1][pos][take] + sum);
}
}
}
cout<<dp[1][0][0]<<"\n";
return 0;
}
