#include<stdio.h>
void merge(int a[],int b[],int c[],int d[],int left,int mid,int right)
{
    int i=left,j=mid+1;
    int k=left;
    while((i<=mid)&&(j<=right))
    {
        if(a[i]>=a[j])
        {b[k++]=a[i++];
        k--;
        i--;
        d[k++]=c[i++];}
        else
        {b[k++]=a[j++];
        k--;
        j--;
        d[k++]=c[j++];}
    }
    if(i>mid)
        for(int q=j;q<=right;q++)
        {b[k++]=a[q];
    k--;
         d[k++]=c[q];
    }
    else if(j>right)
        for(int q=i;q<=mid;q++)
        {b[k++]=a[q];
    k--;
    d[k++]=c[q];}
    for (int l = left;l <= mid;l++) {
        a[l] = b[l];
        c[l]=d[l];
    }
    for (int l = mid+1;l <= right;l++) {
        a[l] = b[l];
        c[l]=d[l];
    }
}
void mergesort(int a[],int b[],int c[],int d[],int left,int right)
{
    if(left<right)
    {
        int mid = (left + right) / 2;
        mergesort(a,b,c,d,left,mid);
        mergesort(a,b,c,d,mid+1,right);
        merge(a, b,c,d, left, mid, right);
    }
}
int main()
{
    int n,i;
    int c[15000],a[15000],b[15000],d[15000];
    scanf("%d",&n);
    for(i=0;i<n;i++)
    {
        scanf("%d",&c[i]);

        scanf("%d",&a[i]);
    }
    mergesort(a,b,c,d,0,n-1);
    for(i=0;i<n;i++)
    {
        printf("%d %d\n",d[i],b[i]);
    }
    fflush(stdin);
    getchar();
    return 0;
}

I will solve all your issues with all your current non-AC tasks just for 0.01BTC :>

too expensive~

Sorry then :)
Anyways, feel free to look into older threads of corresponding tasks, they might contain hints for your questions.

thank you very much~~