#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n;
	cin >> n;

	vector<ll> b(n);
	rep(i, n) cin >> b[i];

	queue<int> zero;
	queue<int> pos;

	ll ans = 0;
	rep(i, n){
		if(b[i] == 0){
			if(!pos.empty()){
				int j = pos.front();
				pos.pop();
				ans += abs(j - i);
			}else{
				zero.push(i);
			}
		}else if(b[i] >= 2){
			rep(_, b[i] - 1){
				if(!zero.empty()){
					int j = zero.front();
					zero.pop();
					ans += abs(j - i);
				}else{
					pos.push(i);
				}
			}
		}
	}

	assert(zero.empty() && pos.empty());

	cout << ans << endl;	
}