#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;
typedef pair<int,int> pp;
const int INF = 1e9;
const int MOD = 1000000007;


int main() {
    int n;
    cin >> n;
    vector<int> b(n);
    rep(i,n) cin >> b[i];
    int j = 0;
    ll ans = 0;
    rep(i,n){
        if(b[j] > 0){
            ans += abs(j -i);
            b[j] --;
        }
        else{
            while(b[j] == 0) j ++;
            ans += abs(i -j);
            b[j] --;
        }
    }

    cout << ans << endl;

    return 0;  
}