#include <bits/stdc++.h>
using namespace std;
struct block {
int h, c;
};
const int MAX_N = 300;
const int MAX_H = 2 * MAX_N + 3;
const int MAX_COST = 1e9;
const long long INF = 1e15;
block blocks[MAX_N + 1];
long long dp[MAX_H + 1][MAX_N + 1][MAX_N + 1];
vector<int> costsByH[MAX_H + 1];
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;
}
}
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;
priority_queue<int> pq;
int minCost = MAX_COST;
for (int h = minH; h < maxH; h++) {
int extra = costsByH[h + 1].size();
for (int g = 0; g <= n; g++) {
for (int i = 0; i <= n; i++) {
for (int j = 0; j <= i; j++)
dp[h + 1][i - j + extra][max(g - j, 0) + j] = min(dp[h + 1][i - j + extra][max(g - j, 0) + j],
dp[h][i][g] + (long long)k * (i - j) + (long long)minCost * max(j - g, 0));
}
}
/*
for (int i = 0; i <= n; i++) {
for (int g = 0; g <= n; g++)
printf("%lld ", dp[h][i][g]);
printf("\n");
}
printf("\n");
*/
for (int c: costsByH[h])
pq.push(-c);
if (!pq.empty()) {
minCost = min(minCost, -pq.top());
pq.pop();
}
}
long long ans = INF;
for (int g = 0; g <= n; g++)
ans = min(ans, dp[maxH][0][g]);
cout << ans << "\n";
return 0;
}
