func_code_string: #include <bits/stdc++.h>   using namespace std;   const long double pi = acos(-1);   const long long inf = 1e18, M = 1e9 + 7;   const long long int N = 1;   bool left_turn(pair<long long int, long long int> a,                  pair<long long int, long long int> b,                  pair<long long int, long long int> c) {     if (a.first == b.first) {       if (a.second < b.second)         return c.first < b.first;       else         return c.first > b.first;     } else if (a.second == b.second) {       if (a.first < b.first)         return c.second > b.second;       else         return c.second < b.second;     }   }   void solve() {     long long int n;     cin >> n;     vector<pair<long long int, long long int> > v(n + 1);     for (long long int i = 0; i < n + 1; ++i) cin >> v[i].first >> v[i].second;     long long int ans = 0;     for (long long int i = 1; i < n; ++i) {       if (left_turn(v[i - 1], v[i], v[i + 1])) ++ans;     }     cout << ans;   }   int32_t main() {     long long int t = 1;     for (long long int z = 1; z <= t; ++z) {       solve();     }     return 0;   }   