#include <iostream>
#include <vector>
namespace
{
typedef std::vector<int> array_int;
}
int find_turning_number(const array_int& set)
{
if(set.empty()) return -1;
int l(0), r(set.size() - 1), m(-1);
for(; (1 + l) != r ;)
{
m = l + ((r - l) / 2);
if(set[m] > set[r]) r = m;
else if(set[m] < set[r]) l = m;
}
return r;
}
int main()
{
array_int set;
set.push_back(1);
set.push_back(2);
set.push_back(3);
set.push_back(4);
set.push_back(5);
set.push_back(10);
set.push_back(9);
set.push_back(8);
set.push_back(7);
set.push_back(6);
std::cout << find_turning_number(set);
return 0;
}