HDU 4911

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#define M 100007
#define ll _int64
ll a[M],c[M],ans,k;
using namespace std;
void merg(ll a[],int first,int mid,int last,ll c[])
{
    int i=first,j=mid+1;
    int m=mid,n=last;
    k=0;
    while(i<=m||j<=n)
    {
        if(j>n||(i<=m&&a[i]<=a[j])) c[k++]=a[i++];
        else {
            c[k++]=a[j++]; ans+=(m-i+1);
        }
    }
    for(i=0;i<k;i++)
        a[first+i]=c[i];
}
void merge_sort(ll a[], int first,int last,ll c[])
{
    if(first<last)
    {
        int mid=(first+last)>>1;
        merge_sort(a,first,mid,c);
            merge_sort(a,mid+1,last,c);
        merg(a,first,mid,last,c);
    }
}
int main()
{
int  n;
    ll k;
    while(scanf("%d%I64d",&n,&k)!=EOF)
    {
        memset(a,0,sizeof(a));
    memset(c,0,sizeof(c));
    ans=0;
    for(int i=0;i<n;i++)
        scanf("%I64d",&a[i]);
    merge_sort(a,0,n-1,c);
    if(ans-k<=0)
        printf("0\n");
    else printf("%I64d\n",ans-k);
    }
    return 0;
}