// 二分查找法
#include <iostream>
#include <vector>
using namespace std;
int BinarySearch(vector<int> vec,int target)
{
// 特殊输入
if(vec.size() <= 0)
return -1;
// 二分查找(非递归)
int low = 0;
int mid = 0;
int high = vec.size()-1;
// 注意:取等号
while(low <= high)
{
mid = (low + high)/2;
if(vec[mid] == target)
return mid;
if(vec[mid] > target)
high = mid-1;
else
low = mid+1;
}
return -1;
}
int main()
{
vector<int> vec = {1,2,3,5,7,7,7,7,9,10};
int target;
while(cin>>target)
cout<<BinarySearch(vec,target)<<endl;
return 0;
}