#include <iostream>
#include <queue>
using namespace std;
int main(){
    int N;
    long long cnt=0;
    cin >> N;
    vector<int> B(N,0);
    queue<int> Bnone,Ball;
    for(int i=0;i<N;i++){
        cin >> B[i];
        if(B[i]>1)Ball.push(i);
        if(B[i]==0)Bnone.push(i);
    }
    while(!Bnone.empty()){
        int t=Bnone.front();Bnone.pop();
        int s=Ball.front();
        cnt+=abs(t-s);B[s]--;
        if(B[s]==1)Ball.pop();
    }
        
    cout << cnt << endl;
    return 0;
}