#include <bits/stdc++.h>
//using namespace std;

typedef __float128 Int;

int main() {
    std::ios_base::sync_with_stdio(false);
//    freopen("input.txt", "rt", stdin);

    int n;
    std::cin >> n;

    std::vector<int> a(n);
    for (auto & it : a) {
        std::cin >> it;
    }

    std::map<int, int> count;
    count[a.back()] = 1;

    Int answer = 0;
    Int sum = a[n-1];

    for (int i = n-2; i >= 0; --i) {
        Int s = sum;
        int c = n - i - 1;
        {
            auto it = count.find(a[i]);
            if (it != count.end()) {
                s -= (Int) it->second * it->first;
                c -= it->second;
            }
        }

        {
            auto it = count.find(a[i]-1);
            if (it != count.end()) {
                s -= (Int) it->second * it->first;
                c -= it->second;
            }
        }

        {
            auto it = count.find(a[i]+1);
            if (it != count.end()) {
                s -= (Int) it->second * it->first;
                c -= it->second;
            }
        }

        answer += s - (Int)c * a[i];

        count[a[i]]++;
        sum += a[i];
    }

    std::string r;

    if (answer < 0) {
        r += '-';
        answer = -answer;
    }

    long long high = (long long) (answer / 1000000000000000LL);
    long long low = (long long) (answer - (Int)high * 1000000000000000LL);
    if (high > 0) {
        std::cout << r << high << std::setw(15) << std::setfill('0') << low;
    } else {
        std::cout << r << low;
    }

    return 0;
}