#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline string toString(T a) {
  ostringstream os("");
  os << a;
  return os.str();
}
template <typename T>
inline long long toLong(T a) {
  long long res;
  istringstream os(a);
  os >> res;
  return res;
}
template <typename T>
inline T S(T a) {
  return a * a;
}
template <typename T>
inline T gcd(T a, T b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
template <typename T>
inline unsigned long long bigmod(T a, T b, T m) {
  if (b == 0)
    return 1;
  else if (b % 2 == 0)
    return S(bigmod(a, b / 2, m)) % m;
  else
    return (a % m * bigmod(a, b - 1, m)) % m;
}
template <typename T>
inline vector<string> parse(T str) {
  vector<string> res;
  string s;
  istringstream os(str);
  while (os >> s) res.push_back(s);
  return res;
}
template <typename T>
inline unsigned long long dist(T A, T B) {
  unsigned long long res =
      (A.x - B.x) * (A.x - B.x) + (A.y - B.y) * (A.y - B.y);
  return res;
}
template <typename T>
inline double cosAngle(T a, T b, T c) {
  double res = a * a + b * b - c * c;
  res = res / (2 * a * b);
  res = acos(res);
  return res;
}
template <typename T>
inline T power(T base, int po) {
  T res = 1;
  if (base == 0) return 0;
  for (int i = (0); i < (po); i++) res *= base;
  return res;
}
template <typename T>
inline bool isOn(T mask, T pos) {
  return mask & (1 << pos);
}
template <typename T>
inline int Off(T mask, T pos) {
  return mask ^ (1 << pos);
}
template <typename T>
inline int On(T mask, T pos) {
  return mask | (1 << pos);
}
struct Z {
  int len, pro;
  Z(){};
  Z(int _l, int _p) { len = _l, pro = _p; }
  void print() { cout << len << " " << pro << endl; }
};
Z song[50005];
bool operator<(Z A, Z B) {
  return A.len * A.pro * (100 - B.pro) < B.len * B.pro * (100 - A.pro);
};
int main() {
  int i, j, k, x, y;
  int n, m;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d%d", &x, &y);
    song[i] = Z(x, y);
  }
  sort(song + 1, song + 1 + n);
  double expected = 0;
  double res = 0;
  for (i = n; i >= 1; i--) {
    res += song[i].len + (double)(100 - song[i].pro) / 100.0 * expected;
    expected += ((double)song[i].len * (double)song[i].pro) / 100.0;
  }
  cout << setprecision(12) << fixed;
  cout << res << endl;
}
