#include <bits/stdc++.h>
using namespace std;
struct block {
int h, c;
};
const int MAX_N = 300;
const int MAX_H = 4 * MAX_N + 3;
const long long INF = 1e15;
block blocks[MAX_N + 1];
long long dp[MAX_H + 1][MAX_N + 1][MAX_N + 1];
long long minPref[MAX_N + 1][MAX_N + 1];
vector<int> costsByH[MAX_H + 1];
map<int, int> mp;
void simplifyData(int n) {
vector<int> h;
int first = 0, cnt = 1;
for (int i = 0; i < n; i++)
mp[blocks[i].h]++;
while (!mp.empty()) {
auto x = *mp.begin();
mp.erase(x.first);
if (x.second > 1)
mp[x.first + 1] += x.second - 1;
h.push_back(x.first);
}
sort(h.begin(), h.end());
h.resize(unique(h.begin(), h.end()) - h.begin());
for (int i = 0; i < n; i++)
blocks[i].h = lower_bound(h.begin(), h.end(), blocks[i].h) - h.begin();
}
int main() {
int n, k;
long long costInit = 0;
cin >> n >> k;
for (int i = 0; i < n; i++)
cin >> blocks[i].h >> blocks[i].c;
sort(blocks, blocks + n, [](block a, block b) {
if (a.h == b.h)
return a.c < b.c;
return a.h < b.h;
});
for (int i = 1; i < n; i++) {
if (blocks[i].h == blocks[0].h) {
blocks[i].h++;
costInit += k;
}
}
simplifyData(n);
for (int i = 0; i < n; i++)
costsByH[blocks[i].h].push_back(blocks[i].c);
int minH = blocks[0].h, maxH = n + blocks[n - 1].h + 2;
for (int h = 0; h <= maxH; h++) {
for (int i = 0; i <= n; i++) {
for (int g = 0; g <= n; g++)
dp[h][i][g] = INF;
}
}
dp[minH][1][1] = costInit;
int minCost = blocks[0].c;
for (int i = 0; i <= n; i++) {
minPref[i][0] = dp[minH][i][0];
for (int g = 1; g <= n; g++)
minPref[i][g] = min(minPref[i][g - 1], dp[minH][i][g] - (long long)minCost * g);
}
for (int h = minH + 1; h <= maxH; h++) {
int extra = costsByH[h].size();
for (int g = 0; g <= n; g++) {
deque<int> dq;
for (int j = 0; j <= g; j++) {
while (!dq.empty() && dp[h - 1][j][g] <= dp[h - 1][dq.back()][g])
dq.pop_back();
dq.push_back(j);
}
for (int i = extra; i <= n; i++) {
//for (int j = 0; j + i - extra <= n && j <= g; j++)
// dp[h][i][g] = min(dp[h][i][g], dp[h - 1][i - extra + j][g]);
dp[h][i][g] = min(dp[h][i][g], dp[h - 1][dq.front()][g]);
if (dq.front() == i - extra)
dq.pop_front();
if (i - extra + g + 1 <= n) {
while (!dq.empty() && dp[h - 1][i - extra + g + 1][g] <= dp[h - 1][dq.back()][g])
dq.pop_back();
dq.push_back(i - extra + g + 1);
}
if (i - extra + g <= n)
dp[h][i][g] = min(dp[h][i][g], minPref[i - extra + g][g] + (long long)minCost * g);
dp[h][i][g] += (long long)k * (i - extra);
dp[h][i][g] = min(dp[h][i][g], INF);
}
}
/*
for (int i = 0; i <= n; i++) {
for (int g = 0; g <= n; g++)
printf("%lld ", dp[h - 1][i][g]);
printf("\n");
}
printf("\n");
*/
for (int c: costsByH[h - 1])
minCost = min(minCost, c);
for (int i = 0; i <= n; i++) {
minPref[i][0] = dp[h][i][0];
for (int g = 1; g <= n; g++)
minPref[i][g] = min(minPref[i][g - 1], dp[h][i][g] - (long long)minCost * g);
}
}
long long ans = INF;
for (int g = 0; g <= n; g++)
ans = min(ans, dp[maxH][0][g]);
cout << ans << "\n";
return 0;
}
