#include <iostream>
#include <unordered_map>
using namespace std;

int main() {
    int n, ans = 0;
    cin >> n;
    unordered_map<int, int> hashset;
    for (int i = 0; i < n; i++) {
        int cur;
        cin >> cur;
        ans += hashset[cur - 1] + hashset[cur + 1];
        hashset[cur] = 1;
    }
    cout << ans << endl;
    return 0;
}