#include <iostream> using namespace std; int main() { int n, count = 0; cin >> n; int arr[n]; for (int i = 0; i < n; ++i) { cin >> arr[i]; } for (int i = 1; i < n; ++i) { if (arr[i - 1] - arr[i] <= 2) { count++; } } cout << count << endl; return 0; }