#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define INF 1000000000000000000
#define MOD 998244353
#define MAX 1000000

int main(){
  int N;
  cin>>N;
  vector<int> A(N);
  for(int i=0;i<N;i++){
    cin>>A[i];
  }
  vector<int> sum0(N,0),sum1(N,0);
  sum0[N-1]=0;
  sum1[N-1]=0;
  ll ans=0;
  for(int i=N-2;i>=0;i--){
    if(A[i]==1){
      sum1[i]=sum0[i+1]+1;
      ans+=(ll)sum1[i];
    }else{
      sum0[i]=sum1[i+1]+1;
    }
  }
  cout<<ans<<'\n';
}