#include<bits/stdc++.h>
#define taskname "C"
using namespace std;
typedef long long ll;
template<class T>void minimize(T& a, T b){
if(a > b){
a = b;
}
}
const int lim = 305;
int n, k, h[lim], c[lim];
namespace sub1{
void solve(){
int idm = 1;
for(int i = 2; i <= n; i++){
if(h[i] < h[idm] || (h[i] == h[idm] && c[i] < c[idm])){
idm = i;
}
}
ll ans = 0;
for(int i = 1; i <= n; i++){
if(i != idm && h[i] == h[idm]){
ans += k;
h[i]++;
}
}
vector<int>p(n);
iota(p.begin(), p.end(), 1);
sort(p.begin(), p.end(), [&] (int i, int j){
return h[i] > h[j];
});
vector<bool>nuse(n, true);
for(int i = n - 2; i > -1; i--){
bool flag = true;
for(int j = i + 1; j < n; j++){
if(h[p[j]] < h[p[i]] && nuse[p[j]]){
nuse[p[j]] = flag = false;
break;
}
}
if(flag){
int id = idm;
for(int j = i + 1; j < n; j++){
if(h[p[j]] < h[p[i]] && c[p[j]] < c[id]){
id = p[j];
}
}
ans += c[id];
}
}
cout << ans;
}
}
const ll INF = 1e18;
namespace sub34{
const int lim = 42;
const int LIM = lim << 1;
ll f[LIM][lim][lim];
int cnt[LIM], min_cost[LIM];
ll dp(int pos, int bef, int cuse){
if(pos == LIM){
return ll(max(0, bef - cuse)) * min_cost[LIM - 1];
}
ll& ans = f[pos][bef][cuse];
if(ans != -1){
return ans;
}
ans = INF;
bef += cnt[pos];
for(int i = 0; i <= min(cuse, bef); i++){
for(int j = 0; i + j <= bef; j++){
minimize(ans, ll(j) * min_cost[pos - 1] + ll(k) * (bef - i - j) + dp(pos + 1, bef - i - j, cuse + j));
}
}
return ans;
}
void solve(){
int idm = 1;
for(int i = 2; i <= n; i++){
if(h[i] < h[idm] || (h[i] == h[idm] && c[i] < c[idm])){
idm = i;
}
}
ll init_delta = 0;
for(int i = 1; i <= n; i++){
if(i != idm && h[i] == h[idm]){
init_delta += k;
h[i]++;
}
}
memset(min_cost, 0x3f, sizeof(min_cost));
memset(cnt, 0, sizeof(cnt));
for(int i = 1; i <= n; i++){
minimize(min_cost[h[i]], c[i]);
cnt[h[i]]++;
}
for(int i = 1; i < LIM; i++){
minimize(min_cost[i], min_cost[i - 1]);
}
memset(f, -1, sizeof(f));
cout << dp(1, 0, 1) + init_delta;
}
}
namespace sub256{
const int lim = 302;
const int LIM = 3000;
int cnt[LIM], min_cost[LIM];
ll f[lim][lim], pfm[lim][lim];
void solve(){
int idm = 1;
for(int i = 2; i <= n; i++){
if(h[i] < h[idm] || (h[i] == h[idm] && c[i] < c[idm])){
idm = i;
}
}
for(int i = 1, mih = h[idm]; i <= n; i++){
h[i] -= mih;
}
ll init_delta = 0;
map<int, int>big_cnt;
for(int i = 1; i <= n; i++){
if(i != idm && h[i] == h[idm]){
init_delta += k;
h[i]++;
}
big_cnt[h[i]]++;
}
vector<int>comp;
for(int i = 1; i <= n; i++){
for(int j = big_cnt[h[i]] * 5; j > -1; j--){
comp.push_back(h[i] + j);
}
big_cnt[h[i]] = -1;
}
sort(comp.begin(), comp.end());
comp.resize(unique(comp.begin(), comp.end()) - comp.begin());
while(comp.size() <= LIM){
comp.push_back(comp.back() + 1);
}
memset(min_cost, 0x3f, sizeof(min_cost));
memset(cnt, 0, sizeof(cnt));
for(int i = 1; i <= n; i++){
cnt[h[i] = lower_bound(comp.begin(), comp.end(), h[i]) - comp.begin()]++;
minimize(min_cost[h[i]], c[i]);
}
for(int i = 1; i < LIM; i++){
minimize(min_cost[i], min_cost[i - 1]);
}
for(int bef = 0; bef <= n; bef++){
for(int cuse = 0; cuse <= n; cuse++){
f[bef][cuse] = ll(max(0, bef - cuse)) * min_cost[LIM - 1];
}
}
for(int pos = LIM - 1; pos > 0; pos--){
for(int sum = 0; sum <= n; sum++){
ll cmin = INF;
for(int bef = 0; bef <= sum; pfm[sum][bef++] = cmin){
minimize(cmin, ll(k) * (comp[pos + 1] - comp[pos]) * bef + ll(min_cost[pos - 1]) * (lim - bef) + f[bef][sum - bef]);
}
}
for(int bef = cnt[pos]; bef <= n; bef++){
for(int cuse = 0; bef + cuse <= n; cuse++){
int nbef = bef - min(bef, cuse);
f[bef - cnt[pos]][cuse] = min(pfm[bef + cuse][bef] - ll(lim - bef) * min_cost[pos - 1], pfm[nbef + cuse][nbef] - ll(lim - nbef) * min_cost[pos - 1]);
}
}
}
cout << f[0][1] + init_delta;
}
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
if(fopen(taskname".inp", "r")){
freopen(taskname".inp", "r", stdin);
}
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> h[i] >> c[i];
}
if(k >= 100000 && *max_element(h + 1, h + n + 1) <= 300 && *max_element(c + 1, c + n + 1) <= 100){
sub1::solve();
}
else if(n <= 40 && *max_element(h + 1, h + n + 1) <= 40){
sub34::solve();
}
else{
sub256::solve();
}
}
