//
//  main.cpp
//  Sort Binary Array
//
//  Created by Himanshu on 06/04/22.
//
 
#include <iostream>
using namespace std;
 
int solve (int arr[], int n) {
    int ans = 0;
    int currOnePos = n-1;
 
    for (int index=n-1; index>=0; index--) {
        if (arr[index] == 1) {
            ans += currOnePos-index;
            currOnePos--;
        }
    }
    return ans;
}
 
int main() {
 
    int n;
    cin>>n;
 
    int *arr = new int[n]();
 
    for (int i=0; i<n; i++) {
        cin>>arr[i];
    }
 
    cout<<solve(arr, n)<<endl;
 
    return 0;
}
 

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7
1 1 0 0 0 1 0