SFSA

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<iostream>
#include<algorithm>
#include<queue>
#include<stack>
const int MAXN=1e4+15;
#define ll long long
using namespace std;
ll f[MAXN];
int sum[MAXN],sumtimee[MAXN];
int num[MAXN];
int n,m;
int s;
int tail,head,que[MAXN];

int i;
int main(){
	scanf("%d%d",&n,&s);
	for(i=1;i<=n;i++)
	{
		scanf("%d%d",&sumtimee[i],&num[i]);
		sum[i]=sum[i-1]+num[i];sumtimee[i]=sumtimee[i-1]+sumtimee[i];
	}
	head=tail=1;
	que[tail++]=0;
	for(i=1;i<=n;i++)
	{
		while(head+1<tail&&(f[que[head+1]]-f[que[head]])<=(s+sumtimee[i])*(sum[que[head+1]]-sum[que[head]]))
		head++;
		int k=que[head];
		f[i]=f[k]-(s+sumtimee[i])*sum[k]+sumtimee[i]*sum[i]+s*sum[n];

		while(head+1<tail&&(f[i]-f[que[tail-1]])*(num[que[tail-1]]-num[que[tail-2]])<=(num[i]-num[que[tail-1]])*(f[que[tail-1]]-f[que[tail-2]]))
		tail--;
		que[tail++]=i;
	}
	printf("%lld",f[n]);
	return 0;
}