#include <bits/stdc++.h>
#define int long long
using namespace std;
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
std::mt19937 rng(std::chrono::steady_clock::now().time_since_epoch().count());
const int MOD=1e18;
const int MX=301;
void solve() {
int dp[MX][MX][MX];//guarda aonde eu to,ultima base de subir que peguei e quantos ta no bolso
int n,m;cin>>n>>m;
L(i,0,n){
L(j,0,n){
L(k,0,n){
dp[i][j][k]=MOD;
}
}
}
vector<int> h(n);
vector<int> c(n);
vector<int> ord(n);iota(all(ord),0);
L(i,0,n-1){
cin>>h[i]>>c[i];
}
sort(all(ord),[&](int a, int b){
if(h[a]==h[b])return c[a]>c[b];
return h[a]<h[b];
});
vector<int> aux(n);
L(i,0,n-1)aux[i]=h[ord[i]];
h=aux;
L(i,0,n-1)aux[i]=c[ord[i]];
c=aux;
vector<bool> pode(n,0);
pode[n-1]=1;
L(i,0,n-2){
if(h[i]!=h[i+1])pode[i]=1;//pode virar uma base de subida
}
dp[n][n][0]=0;
int resp=MOD;
R(i,n-1,0){
L(j,i+1,n){//ultima base
L(k,0,n-1-i){
dp[i][j][k+1]=min(dp[i][j][k+1],dp[i+1][j][k]);//so boto pra esperar
if(pode[i]){
dp[i][j][1]=min(dp[i][j][1],dp[i+1][j][k]+k*c[i]);//esvazio os acumulados pro meu atual
}
if(pode[i])dp[i][i][k+1]=min(dp[i][i][k+1],dp[i+1][j][k]);//transformo em base de subida
if(pode[i]){//posso esvaziar na base de subida tbm
dp[i][i][1]=min(dp[i][i][1],dp[i+1][j][k] +k*c[i]);
}
if(j!=n)dp[i][j][k]=min(dp[i][j][k],dp[i+1][j][k]+(h[j]-h[i]+1)*m + c[j]);//levo pra base de subida
}
}
}//resp eh min dp[0][j][0]-c[j];
int somat=0;
L(i,0,n-1){
L(j,i,n-1){
resp=min(resp,-c[i]+dp[i][j][1]+(h[j]*i-somat+i)*m + c[j]*i);
}
somat+=h[i];
}
cout<<resp;
}
int32_t main() {
std::cin.tie(0)->sync_with_stdio(0);
std::cin.exceptions(std::cin.failbit);
int T = 1;
// std::cin >> T;
while(T--) {
solve();
}
return 0;
}
