#include "bits/stdc++.h"
using namespace std;
#ifdef Nero
#include "Deb.h"
#else
#define debug(...)
#endif
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, k;
cin >> n >> k;
vector<pair<int, int>> a(n);
for (int i = 0; i < n; ++i) {
cin >> a[i].first >> a[i].second;
}
long long ans = 0;
sort(a.begin(), a.end());
for (int i = 1; i < n; ++i) {
if (a[i].first == a[0].first) {
ans += k;
a[i].first++;
}
}
int available = 1;
int mn = a[0].second;
for (int i = 1; i < n; ++i) {
int j = i;
int mn2 = a[i].second;
while (j + 1 < n && a[j + 1].first == a[j].first) {
j++;
mn2 = min(mn2, a[j].second);
}
int cnt = j - i + 1;
ans += max(0, cnt - available) * mn;
available = max(0, available - cnt);
available += cnt;
i = j;
mn = min(mn, mn2);
}
cout << ans << '\n';
return 0;
}
