CodeForces C. Songs Compression

http://codeforces.com/contest/1015/problem/C

Ivan has $\mathrm{nn songs\; on\; his\; phone.\; The\; size\; of\; the ii-th\; song\; is aiai bytes.\; Ivan\; also\; has\; a\; flash\; drive\; which\; can\; hold\; at\; most mm bytes\; in\; total.\; Initially,\; his\; flash\; drive\; is\; empty.}$

Ivan wants to copy all $\mathrm{nn songs\; to\; the\; flash\; drive.\; He\; can\; compress\; the\; songs.\; If\; he\; compresses\; the ii-th\; song,\; the\; size\; of\; the ii-th\; song\; reduces\; from aiai to bibi bytes\; (bi<aibi<ai).}$

Ivan can compress any subset of the songs (possibly empty) and copy all the songs to his flash drive if the sum of their sizes is at most $\mathrm{mm.\; He\; can\; compress any subset\; of\; the\; songs\; (not\; necessarily\; contiguous).}$

Ivan wants to find the minimum number of songs he needs to compress in such a way that all his songs fit on the drive (i.e. the sum of their sizes is less than or equal to $\mathrm{mm).}$

If it is impossible to copy all the songs (even if Ivan compresses all the songs), print "-1". Otherwise print the minimum number of songs Ivan needs to compress.

Input

The first line of the input contains two integers $\mathrm{nn and mm (1\le n\le 105,1\le m\le 1091\le n\le 105,1\le m\le 109)\; —\; the\; number\; of\; the\; songs\; on\; Ivan\text{'}s\; phone\; and\; the\; capacity\; of\; Ivan\text{'}s\; flash\; drive.}$

The next $\mathrm{nn lines\; contain\; two\; integers\; each:\; the ii-th\; line\; contains\; two\; integers aiai and bibi (1\le ai,bi\le 1091\le ai,bi\le 109, ai>biai>bi)\; —\; the\; initial\; size\; of\; the ii-th\; song\; and\; the\; size\; of\; the ii-th\; song\; after\; compression.}$

Output

If it is impossible to compress a subset of the songs in such a way that all songs fit on the flash drive, print "-1". Otherwise print the minimum number of the songs to compress.

Examples

input

Copy

4 21
10 8
7 4
3 1
5 4

output

Copy

2

input

Copy

4 16
10 8
7 4
3 1
5 4

output

Copy

-1

代码：

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e5 + 10;
int N, M;
long long sum1 = 0, sum2 = 0;

struct Node{
    int s;
    int e;
    int t;
}node[maxn];

bool cmp(const Node& a, const Node& b) {
    return a.t > b.t;
}

int main() {
    scanf("%d%d", &N, &M);
    for(int i = 1; i <= N; i ++) {
        scanf("%d%d", &node[i].s, &node[i].e);
        sum1 += node[i].e;
        sum2 += node[i].s;
        node[i].t = node[i].s - node[i].e;
    }

    if(sum1 > M) {
        printf("-1
");
        return 0;
    }
    if(sum2 <= M) {
        printf("0
");
        return 0;
    }

    int ans = 0;
    sort(node + 1, node + 1 + N, cmp);
    for(int i = 1; i <= N; i ++) {
        sum2 -= node[i].t;
        ans ++;
        if(sum2 <= M)
            break;
    }
    printf("%d
", ans);
    return 0;
}