#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#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 T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }

} // namespace n91
#include <cassert>
#include <stack>

namespace nimi {

  template <class T, class Op> class queue_aggregation {
  private:
    class node {
    public:
      T val, sum;
      node(const T& val, const T& sum) : val(val), sum(sum) {}
    };

    Op op;
    std::stack<node> front_stack, back_stack;

  public:
    queue_aggregation(const Op& op = Op())
      : op(op), front_stack(), back_stack() {}

    bool empty() const { return front_stack.empty() && back_stack.empty(); }

    std::size_t size() const { return front_stack.size() + back_stack.size(); }

    T fold_all() const {
      assert(!empty());
      if (front_stack.empty()) {
        return back_stack.top().sum;
      }
      else if (back_stack.empty()) {
        return front_stack.top().sum;
      }
      else {
        return op(front_stack.top().sum, back_stack.top().sum);
      }
    }

    void push(const T& x) {
      if (back_stack.empty()) {
        back_stack.emplace(x, x);
      }
      else {
        T s{ op(back_stack.top().sum, x) };
        back_stack.emplace(x, s);
      }
    }

    void pop() {
      assert(!empty());
      if (front_stack.empty()) {
        front_stack.emplace(back_stack.top().val, back_stack.top().val);
        back_stack.pop();
        while (!back_stack.empty()) {
          T s{ op(back_stack.top().val, front_stack.top().sum) };
          front_stack.emplace(back_stack.top().val, s);
          back_stack.pop();
        }
      }
      front_stack.pop();
    }
  };

} // namespace nimi

#include <algorithm>
#include <iostream>
#include <utility>

namespace n91 {

  void main_() {
    while (true) {
      static constexpr i64 Inf = std::numeric_limits<i64>::max() / 10;
      const usize n{ scan<usize>() };
      if (n == 0) {
        return;
      }
      struct city_t {
        i64 p;
        usize d;
      };
      std::vector<city_t> city(n);
      for (auto& e : city) {
        std::cin >> e.p >> e.d;
      }
      std::sort(city.begin(), city.end(),
        [](auto l, auto r) { return l.p < r.p; });
      if (n == 2) {
        std::cout << city[1].p - city[0].p << std::endl;
        continue;
      }
      std::vector<city_t> leaf, path;

      usize degree_sum = 0;
      for (const auto& e : city) {
        if (e.d == 1) {
          leaf.push_back(e);
        }
        else {
          path.push_back(e);
        }
        degree_sum += e.d;
      }
      if (degree_sum < 2 * n - 2) {
        std::cout << "-1" << std::endl;
        continue;
      }
      i64 ans = path.back().p - path.front().p;
      const usize pn = path.size();
      const usize ln = leaf.size();
      for (const auto i : rep(1, pn)) {
        path[i - 1].d -= 1;
        path[i].d -= 1;
      }
      std::vector<i64> dp(ln + 1, Inf);
      dp[0] = 0;
      const auto min = [](const i64 l, const i64 r) { return std::min(l, r); };
      for (const auto& e : path) {
        nimi::queue_aggregation<i64, decltype(min)> que(min);
        i64 dsum = 0;
        for (const auto i : rep(0, ln + 1)) {
          if (i != 0) {
            dsum += std::abs(e.p - leaf[i - 1].p);
          }
          if (que.size() > e.d) {
            que.pop();
          }
          que.push(dp[i] - dsum);
          dp[i] = dsum + que.fold_all();
        }
      }
      std::cout << ans + dp[ln] << std::endl;
    }
  }

} // namespace n91

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



Measured memory_bytes: 3152