蓝桥——训练士兵

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e5+10; 
struct node{
	int p,c;
	bool operator < (const node &x) const{
		return c<x.c;
	}
}a[N];
int n,s;
int sp[N],scp[N];
int getp(int l,int r){
	return sp[r]-sp[l-1];
}
int getscp(int l,int r){
	return scp[r]-scp[l-1];
}
signed main(){
	cin>>n>>s;
	for(int i=1;i<=n;++i){
		cin>>a[i].p>>a[i].c;
	}
	sort(a+1,a+n+1);
	for(int i=1;i<=n;++i){
		sp[i]=sp[i-1]+a[i].p;
		scp[i]=scp[i-1]+a[i].c*a[i].p;
	}
	int ans=0x3f3f3f3f3f3f3f3f;
	for(int i=0;i<=n;++i){
		int now=a[i].c*s+getscp(i+1,n)-a[i].c*getp(i+1,n);
		ans=min(ans,now);
	}
	cout<<ans<<endl;
	return 0;
}