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

unordered_set<int> s;

int main(){
    int n, ans = 0;
    scanf("%d", &n);
    for(int i = 0; i < n; i++){
        int x;
        scanf("%d", &x);
        if(s.count(x - 1)) ans++;
        if(s.count(x + 1)) ans++;
        s.insert(x);
    }
    cout << ans;
    return 0;
}