> 用C++STL sort()排序不一定能过，我已经试了，原因不明，

水过啊

#include <algorithm>
#include <iostream>
#include <string>
#include <queue>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>

#define N 50010

using namespace std;

struct cows
{
    int i, a, b;
} c[N];

bool cmp1(cows a, cows b)
{
    return a.a > b.a;
}

bool cmp2(cows a, cows b)
{
    return a.b > b.b;
}

int main()
{
    int n, k, a, b;
    int i;
    scanf("%d %d", &n, &k);
    for(i=0; i<n; ++i)
    {
        scanf("%d %d", &a, &b);
        c[i].i = i + 1;
        c[i].a = a;
        c[i].b = b;
    }
    sort(c, c+n, cmp1);
    sort(c, c+k, cmp2);
    printf("%d\n", c[0].i);
    return 0;
}