#include<iostream>
using namespace std;
int countOfNumFromSortArr(int arr[],int len,int num);
int main()
{
int arr[]={0,1,1,2,2,2,2,3,3,3,4};
int n;
cin>>n;
cout<<countOfNumFromSortArr(arr,sizeof(arr)/sizeof(int),n)<<endl;
return 0;
}
int countOfNumFromSortArr(int arr[],int len,int num)
{
if(arr==NULL||len==0)
return -1;
int left=0;
int right=len-1;
int mid;
while(left<=right) // 查找算法的复杂度为lg(n)
{
mid=(left+right)/2;
if(arr[mid]==num)// 找到该数字;
break;
else if(arr[mid]>num)
right=mid-1;
else
left=mid+1;
}
if(left>right)// 没有找到该数字
return 0;
int first;int last; //用来记录num的第一个和最后一个下标
int mid_left,mid_right;
if(arr[mid-1]!=num)
first=mid;
else
{
left=0;
right=mid-1; // 上面找到的Num的位置
while(right-left!=1) // 关键1
{
mid_left=(left+right)/2;
if(arr[mid_left]==num)
right=mid_left; // 关键2
else
left=mid_left;
}
if(arr[left]==num)
first=left;
else
first=right;
}
if(arr[mid+1]!=num)
last=mid;
else
{
left=mid+1;
right=len-1;
while(right-left!=1)
{
mid_right=(left+right)/2;
if(arr[mid_right]==num)
left=mid_right;
else
right=mid_right;
}
if(arr[right]==num)
last=right;
else
last=left;
}
return last-first+1;
}