Juanzhang

#include <cstdio>
using namespace std;

typedef double db;
typedef long long ll;
const int maxn = 1e4 + 10;
ll f[maxn];
int n, S, F[maxn], T[maxn], Q[maxn];

inline db slope(int x, int y) {
  return db(f[x] - f[y]) / db(T[x] - T[y]);
}

int main() {
  scanf("%d %d", &n, &S);
  for (int i = 1; i <= n; i++) {
    scanf("%d %d", T + i, F + i);
  }
  for (int i = n - 1; i; i--) {
    T[i] += T[i + 1], F[i] += F[i + 1];
  }
  int l = 1, r = 1;
  for (int i = n; i; i--) {
    while (l < r && slope(Q[l], Q[l + 1]) < F[i]) l++;
    f[i] = f[Q[l]] + 1ll * F[i] * (S + T[i] - T[Q[l]]);
    while (l < r && slope(Q[r], Q[r - 1]) > slope(Q[r], i)) r--;
    Q[++r] = i;
  }
  printf("%lld", f[1]);
  return 0;
}