#include using namespace std; #include using namespace atcoder; #define rep(i, n) for (ll i = 0; i < (n); ++i) #define rep1(i, n) for (ll i = 1; i <= n; ++i) #define reps(i, s, e) for (ll i = s; i <= e; ++i) #define rrep(i, n) for (ll i = n - 1; 0 <= i; --i) #define all(v) v.begin(), v.end() template bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; } template bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; } using ll = long long; using ld = long double; using cp = complex; using pa = pair; using tup = tuple; using vp = vector >; using vtup = vector >; using st = string; using vs = vector; using vc = vector; using vvi = vector >; using vvc = vector >; using vi = vector; const ll MOD1 = 1000000007; const ll MOD2 = 998244353; const ll INF = (1LL << 60); int main() { ios_base::sync_with_stdio(false); cin.tie(NULL); ll n; cin >> n; vi a(n); rep(i, n) cin >> a[i]; auto b = a; for (int i = 1; i < n; i += 2) b[i] ^= 1; b.push_back(-1); ll pre = n; vi c(n); for (int i = n - 1; 0<= i; i--) { if (b[i] != b[pre]) pre = i; c[i] = pre + 1; } ll ans = 0; rep(i, n) if (a[i]) ans += min(c[i], n - 1) - i; cout << ans << endl; }