#include <bits/stdc++.h>
using namespace std;
template <class T>
void chmax(T& a, const T& b) {
  a = max(a, b);
}
template <class T>
void chmin(T& a, const T& b) {
  a = min(a, b);
}
template <class T>
void uniq(vector<T>& c) {
  sort(c.begin(), c.end());
  c.erase(unique(c.begin(), c.end()), c.end());
}
template <class T>
string to_s(const T& a) {
  ostringstream os;
  os << a;
  return os.str();
}
template <class T>
T to_T(const string& s) {
  istringstream is(s);
  T res;
  is >> res;
  return res;
}
template <class T, class U>
ostream& operator<<(ostream& os, pair<T, U>& p) {
  os << "( " << p.first << ", " << p.second << " )";
  return os;
}
template <class T>
void print(T a, int n, const string& deli = " ", int br = 1) {
  for (int i = 0; i < n; ++i) {
    cout << a[i];
    if (i + 1 != n) cout << deli;
  }
  while (br--) cout << endl;
}
template <class T>
void print(const T& c, const string& deli = " ", int br = 1) {
  for (__typeof__((c).begin()) it = (c).begin(); it != (c).end(); ++it) {
    cout << *it;
    if (++it != c.end()) cout << deli;
    --it;
  }
  while (br--) cout << endl;
}
template <class T>
void print2d(T a, int w, int h, int width = -1, int br = 1) {
  for (int i = 0; i < h; ++i) {
    for (int j = 0; j < w; ++j) {
      if (width != -1) cout.width(width);
      cout << a[i][j] << ' ';
    }
    cout << endl;
  }
  while (br--) cout << endl;
}
template <class T>
void input(T& a, int n) {
  for (int i = 0; i < n; ++i) cin >> a[i];
}
template <class T>
void input(T* a, int n) {
  for (int i = 0; i < n; ++i) cin >> a[i];
}
void fix_pre(int n) {
  cout.setf(ios::fixed, ios::floatfield);
  cout.precision(10);
}
void fast_io() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}
bool in_rect(int x, int y, int w, int h) {
  return 0 <= x && x < w && 0 <= y && y < h;
}
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
const double PI = acos(-1.0);
const int mod = ((long long)(1e9)) + 7;
const int M = 5 * ((long long)(1e4));
int n, len[M], p[M];
bool cmp(int i, int j) {
  return len[i] * p[i] * (100 - p[j]) > len[j] * p[j] * (100 - p[i]);
}
int main() {
  fast_io();
  cin >> n;
  for (int i = 0; i < (int)(n); ++i) cin >> len[i] >> p[i];
  vector<int> idx(n);
  for (int i = 0; i < (int)(n); ++i) idx[i] = i;
  sort((idx).begin(), (idx).end(), cmp);
  double res = accumulate(len, len + n, 0.0);
  double sum = 0;
  for (int i = 0; i < (int)(n); ++i) {
    double pp = p[idx[i]] / 100.0;
    res += (1 - pp) * sum;
    sum += len[idx[i]] * pp;
  }
  fix_pre(10);
  cout << res << endl;
}
