#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<bitset>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<deque>
#include<list>
#include<iomanip>
#include<cmath>
#include<cstring>
#include<functional>
#include<cstdio>
#include<cstdlib>
using namespace std;

#define repr(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) repr(i, 0, n)
#define INF 2e9
//#define MOD 1000000007
#define MOD 998244353
#define LINF (long long)4e18
#define jck 3.141592

const double EPS = 1e-10;

using ll = long long;
using Pi = pair<int,int>;
using Pl = pair<ll,ll>;

int main(){
    int N; cin >> N;
    vector<int> B(N);
    rep(i,N) cin >> B[i];
    set<int> st;
    rep(i,N){
        if(B[i] == 0) st.insert(i);
    }
    ll ans = 0;
    rep(i,N){
        if(B[i] > 1){
            int d = B[i]-1;
            int cnt = 0;
            for(int u : st){
                ans += abs(i-u);
                cnt++;
                st.erase(u);
                if(cnt == d) break;
            }
        }
    }
    cout << ans << endl;
}