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

typedef long long ll;
//typedef modint1000000007 mint;
const int MOD = 1000000007;
#define all(x) x.begin(), x.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
const int inf = 1 << 30;
const ll INF = 1LL << 60;
const int dx[8] = {1, 0, -1, 0, -1, -1, 1, 1};
const int dy[8] = {0, 1, 0, -1, -1, 1, -1, 1};
template <class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template <class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i, n) cin >> a[i];

    vector<int> vec;
    rep(i, n) if(a[i] > 1) vec.push_back(i);

    ll ans = 0;
    int x = 0;
    rep(i, n){
        if(a[i] == 0){
            ans += abs(vec[x] - i);
            a[vec[x]]--;
            a[i]++;
            if(a[vec[x]] <= 1) x++;
        }
    }

    cout << ans << endl;

    return 0;
}