poj 3262 Protecting the Flowers

#include <iostream>#include <cstdio>#include <cstring>#include <set>#include <queue>#include <algorithm>#define MAXN 111111#define MAXM 222222#define INF 1000000000using namespace std;struct node{    int x, y;}a[MAXN];int n;bool cmp(node x, node y){    return x.x * y.y < x.y * y.x;}int main(){    scanf("%d", &n);    for(int i = 0; i < n; i++)    {        scanf("%d%d", &a[i].x, &a[i].y);        a[i].x *= 2;    }    sort(a, a + n, cmp);    long long ans = 0;    long long sum = 0;    for(int i = 0; i < n; i++)    {        ans += sum * (long long)a[i].y;        sum += a[i].x;    }    printf("%I64dn", ans);    return 0;}