//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  struct rep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { ++i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  struct revrep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { --i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) noexcept {
    return a < b ? b - a : a - b;
  }
  template <class T> void chmin(T& a, const T& b) noexcept {
    if (b < a)
      a = b;
  }
  template <class T> void chmax(T& a, const T& b) noexcept {
    if (a < b)
      a = b;
  }
  template <class F> class rec_lambda {
    F f;

  public:
    rec_lambda(F&& f) : f(std::move(f)) {}
    template <class... Args> auto operator()(Args&&... args) const {
      return f(*this, std::forward<Args>(args)...);
    }
  };
  template <class F> auto make_rec(F&& f) { return rec_lambda<F>(std::move(f)); }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }
  constexpr char eoln = '\n';
  template <class T> T ceildiv(const T& l, const T& r) {
    return l / r + (l % r != 0 ? 1 : 0);
  }

} // namespace n91
#include <cstdint>

template <std::uint_fast64_t mod> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 v;

  constexpr modint(const u64 x = 0) noexcept : v(x% mod) {}
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint& operator+=(const modint rhs) noexcept {
    v += rhs.v;
    if (v >= mod)
      v -= mod;
    return *this;
  }
  constexpr modint& operator-=(const modint rhs) noexcept {
    if (v < rhs.v)
      v += mod;
    v -= rhs.v;
    return *this;
  }
  constexpr modint& operator*=(const modint rhs) noexcept {
    v = v * rhs.v % mod;
    return *this;
  }
  constexpr modint& operator/=(modint rhs) noexcept {
    u64 exp = mod - 2;
    while (exp != 0) {
      if (exp % 2 != 0)
        *this *= rhs;
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
};

#include <utility>
#include <vector>

namespace n91 {

  template <class T>
  std::vector<std::pair<T, std::size_t>>
    run_length_encoding(const std::vector<T>& a) {
    if (a.empty()) {
      return std::vector<std::pair<T, std::size_t>>();
    }
    std::vector<std::pair<T, std::size_t>> ret;
    ret.reserve(a.size());
    ret.emplace_back(a.front(), static_cast<std::size_t>(0));
    for (const T& e : a) {
      if (e != ret.back().first) {
        ret.emplace_back(e, static_cast<std::size_t>(0));
      }
      ++ret.back().second;
    }
    ret.shrink_to_fit();
    return std::move(ret);
  }

} // namespace n91

namespace n91 {

  void main_() {
    /*
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    //*/
    const std::string t = scan<std::string>();
    const usize n = t.size();
    std::vector<int> a(n);
    for (const usize i : rep(0, n)) {
      a[i] = t[i] == '1';
    }
    auto b = run_length_encoding(a);
    u64 ans = 0;
    u64 erased = 0;
    usize idx = 0;
    for (const auto e : b) {
      if (e.first == 1) {
        for (const usize i : rep(0, e.second)) {
          if ((idx - erased + i) % 2 == 0) {
            ans += n - (idx + i);
          }
          if ((idx + i) % 2 == 0) {
            ans += (erased + 1) / 2;
          }
          else {
            ans += (erased / 2);
          }
        }
      }
      else {
        if ((idx - erased) % 2 == 0) {
          erased += e.second;
        }
        else {
          erased += e.second - 1;
        }
      }
      idx += e.second;
    }
    std::cout << ans << eoln;
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 7624