#include <bits/stdc++.h> using namespace std; typedef long long int ll; typedef pair<ll,ll> P; typedef vector<ll> VI; typedef vector<VI> VVI; #define REP(i,n) for(ll i=0;i<(n);i++) #define ALL(v) v.begin(),v.end() template<typename T> bool chmax(T &x, const T &y) {return (x<y)?(x=y,true):false;}; template<typename T> bool chmin(T &x, const T &y) {return (x>y)?(x=y,true):false;}; constexpr ll MOD=1000000007; constexpr ll INF=2e18; int main(){ int n; cin >> n; VI a(n); REP(i,n) cin >> a[i]; REP(i,n){ if(i%2==1) a[i]=!a[i]; } int x=0; ll ans=0; for(int i=n-1;i>=0;i--){ if(i<n-1){ if(a[i]==a[i+1]) x++; else x=1; } if(i%2!=a[i]) ans+=x; } cout << ans << endl; return 0; }