20140901.cpp

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int main(){
    int n;
    cin >> n;
    vector<int> v(n);
    for (int i = 0; i < n; ++i){
        scanf("%d", &v[i]);
    }
    sort(v.begin(), v.end());
    int cnt = 0;
    for (int i = 0; i < n - 1;++i){
        if(v[i+1]-v[i]==1)
            ++cnt;
    }
    cout << cnt;
}