#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
/*
knew beforehand that it was dp
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
ll n,k; cin >> n >> k;
vector<pll> a(n+5);
rep1(i,n) cin >> a[i].ff >> a[i].ss;
sort(a.begin()+1,a.begin()+n+1);
ll m = n;
auto b = a;
ll add_cost = 0;
rep1(i,n){
if(i == 1) conts;
if(b[i].ff <= b[1].ff){
ll add = b[1].ff-b[i].ff+1;
b[i].ff += add;
add_cost += add*k;
}
}
sort(b.begin()+1,b.begin()+n+1);
vector<pll> c,d;
c.pb({0,0}), d.pb({0,0});
ll mn = inf2;
rep1(i,n){
if(b[i].ss < mn){
d.pb(b[i]);
mn = b[i].ss;
}
else{
c.pb(b[i]);
}
}
ll siz1 = sz(c)-1, siz2 = sz(d)-1;
c.pb({inf2,-1});
ll dp[siz1+5][m+5][n+5];
memset(dp,0x3f,sizeof dp);
dp[1][max(d[1].ff-c[1].ff+1,0ll)][1] = 0;
rep1(i,siz1){
rep(h,m+1){
ll mn_cost = inf2;
ll nxth = inf2;
rep1(j,siz2){
auto [height,cost] = d[j];
if(height > h-1+c[i].ff){
amin(nxth,height);
}
else{
amin(mn_cost,cost);
}
}
// place from c[i]
rep(f,n+1){
if(dp[i][h][f] > inf2) conts;
ll sumh = 0;
for(int j = i; j <= siz1; ++j){
sumh += c[j].ff;
ll h2 = max((ll)h+1+c[i].ff-1,c[j].ff);
if(h2 > nxth) break;
ll curr_sum = sumh, curr_cnt = j-i+1;
if(h2 == nxth){
curr_sum += nxth;
curr_cnt++;
}
ll sub = min((ll)f,curr_cnt);
ll f2 = f-sub+curr_cnt;
ll curr_cost = (curr_cnt-sub)*mn_cost;
curr_cost += (curr_cnt*h2-curr_sum)*k;
amin(dp[j+1][max(h2-c[j+1].ff+1,0ll)][f2],dp[i][h][f]+curr_cost);
}
}
// place from d[i] (nxth)
if(nxth != inf2){
rep(f,n+1){
ll f2 = f;
ll curr_cost = 0;
if(f2 == 0){
curr_cost += mn_cost;
}
else{
f2--;
}
f2++;
amin(dp[i][max(nxth-c[i].ff+1,0ll)][f2],dp[i][h][f]+curr_cost);
}
}
}
}
ll ans = inf2;
rep(h,m+5){
rep(f,n+5){
ll val = dp[siz1+1][h][f];
amin(ans,dp[siz1+1][h][f]);
}
}
ans += add_cost;
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
