#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <iomanip>
using namespace std;
using ll = long long;

int main() {
    int n;
    cin >> n;
    vector<int> b(n);
    for(int i = 0; i < n; i++) cin >> b[i];
    int sum = 0;
    ll ans = 0;
    for(int i = 0; i < n - 1; i++) {
        sum += b[i];
        ans += abs(i + 1 - sum);
    }
    cout << ans << endl;
    return 0;
}