【bzoj1597】 土地购买

// bzoj1597
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf 1e18
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

const int maxn=50010;
struct data {LL x,y;}a[maxn];
LL f[maxn];
int n,q[maxn];

bool cmp(data a,data b) {
	return a.x==b.x ? a.y<b.y : a.x<b.x;
}
double slope(int i,int j) {
	return (double)(f[i]-f[j])/(double)(a[i+1].y-a[j+1].y);
}
int main() {
	scanf("%d",&n);
	for (int i=1;i<=n;i++) scanf("%lld%lld",&a[i].x,&a[i].y);
	sort(a+1,a+1+n,cmp);
	int tot=0;
	for (int i=1;i<=n;i++) {
		while (tot &&  a[i].y>=a[tot].y) tot--;
		a[++tot]=a[i];
	}
	n=tot;
	int l=1,r=1;q[1]=0;
	for (int i=1;i<=n;i++) {
		while (l<r && slope(q[l],q[l+1])>=-a[i].x) l++;
		f[i]=f[q[l]]+a[i].x*a[q[l]+1].y;
		while (l<r && slope(q[r-1],q[r])<slope(q[r],i)) r--;
		q[++r]=i;
	}
	printf("%lld",f[n]);
	return 0;
}