#include<cstring>

#include<iostream>

#include<cstdio>

#include<algorithm>

#include<queue>

#include<map>

#include<cmath>

#define rep(i,l,r) for (int i=l;i<=r;i++)

#define down(i,l,r) for (int i=l;i>=r;i--)

#define clr(x,y) memset(x,y,sizeof(x))

#define maxn 300500

#define inf int(1e9)

#define ll long long

using namespace std;

struct data{int x,k,id;ll y;

}a[maxn],s[maxn],t[maxn];

int n,S;

ll f[maxn],bin[];

int cross(data a,data b,data c){

    int x1=b.x-a.x,x2=c.x-a.x;

    ll y1=b.y-a.y,y2=c.y-a.y;

    if ((x1<)^(x2<)) return y1*x2<=y2*x1;

    else return x1*y2-x2*y1<=;

}

bool jud(data a,data b,int k){

    ll x=b.x-a.x,y=b.y-a.y;

    if (x<) return y>x*k;

    else return y<x*k;

}

int read(){

    int x=,f=; char ch=getchar();

    while (!isdigit(ch)){if (ch=='-') f=-; ch=getchar();}

    while (isdigit(ch)){x=x*+ch-''; ch=getchar();}

    return x*f;

}

void cdq(int l,int r){

    if (l==r) {

        a[l].y=f[l];

        return;

    }

    int l1=l,l2=(l+r)/+,mid=(l+r)/;

    rep(i,l,r) if (a[i].id<=mid) t[l1++]=a[i]; else t[l2++]=a[i];

    rep(i,l,r) a[i]=t[i];

    cdq(l,mid);

    int top=;

    rep(i,l,mid){

        while (top>&&cross(s[top-],s[top],a[i])) top--;

        s[++top]=a[i];

    }

    int j=;

    rep(i,mid+,r){

        while (j<top&&jud(s[j],s[j+],a[i].k)) j++;

        f[a[i].id]=min(f[a[i].id],1LL*a[i].k*(a[i].x-s[j].x+S)+f[s[j].id]);

    }

    cdq(mid+,r);

    l1=l,l2=mid+;

    rep(i,l,r) if (l1<=mid&&(a[l1].x<a[l2].x||l2>r)) t[i]=a[l1++]; else t[i]=a[l2++];

    rep(i,l,r) a[i]=t[i];

}

int main(){

    n=read(); S=read();

    rep(i,,n) a[i].x=read(),a[i].k=read();

    down(i,n,) a[i].x+=a[i+].x,a[i].k+=a[i+].k;

    rep(i,,n/) swap(a[i],a[n-i+]);

    rep(i,,n) f[i]=1LL*a[i].k*(a[i].x+S),a[i].id=i; f[]=;

    cdq(,n);

    printf("%lld\n",f[n]);

    return ;

}