#include <bits/stdc++.h>
using namespace std;
const double pi = acos(0.0) * 2.0;
const double eps = 1e-12;
const int step[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
template <class T>
inline T abs1(T a) {
  return a < 0 ? -a : a;
}
template <class T>
inline T max1(T a, T b) {
  return a > b ? a : b;
}
template <class T>
inline T min1(T a, T b) {
  return a < b ? a : b;
}
template <class T>
inline T gcd1(T a, T b) {
  if (a < b) swap(a, b);
  if (a % b == 0) return b;
  return gcd1(b, a % b);
}
template <class T>
inline T lb(T num) {
  return num & (-num);
}
inline int jud(double a, double b) {
  if (abs1(a - b) < eps) return 0;
  if (a < b) return -1;
  return 1;
}
template <class t>
inline int find(t val, t *a, int na, bool f_small = 1, bool f_lb = 1) {
  if (na == 1) return 0;
  int be = 0, en = na - 1;
  if (a[0] <= a[na - 1]) {
    if (f_lb == 0)
      while (be < en) {
        int mid = (be + en + 1) / 2;
        if (jud(a[mid], val) != 1)
          be = mid;
        else
          en = mid - 1;
      }
    else
      while (be < en) {
        int mid = (be + en) / 2;
        if (jud(a[mid], val) != -1)
          en = mid;
        else
          be = mid + 1;
      }
    if (f_small && jud(a[be], val) == 1 && be != 0) be--;
    if (!f_small && jud(a[be], val) == -1 && be != na - 1) be++;
  } else {
    if (f_lb)
      while (be < en) {
        int mid = (be + en + 1) / 2;
        if (jud(a[mid], val) != -1)
          be = mid;
        else
          en = mid - 1;
      }
    else
      while (be < en) {
        int mid = (be + en) / 2;
        if (jud(a[mid], val) != 1)
          en = mid;
        else
          be = mid + 1;
      }
    if (!f_small && jud(a[be], val) == -1 && be != 0) be--;
    if (f_small && jud(a[be], val) == 1 && be != na - 1) be++;
  }
  return be;
}
inline int bitnum(unsigned long long nValue) {
  nValue = ((0xaaaaaaaaaaaaaaaaull & nValue) >> 1) +
           (0x5555555555555555ull & nValue);
  nValue = ((0xccccccccccccccccull & nValue) >> 2) +
           (0x3333333333333333ull & nValue);
  nValue = ((0xf0f0f0f0f0f0f0f0ull & nValue) >> 4) +
           (0x0f0f0f0f0f0f0f0full & nValue);
  nValue = ((0xff00ff00ff00ff00ull & nValue) >> 8) +
           (0x00ff00ff00ff00ffull & nValue);
  nValue = ((0xffff0000ffff0000ull & nValue) >> 16) +
           (0x0000ffff0000ffffull & nValue);
  nValue = ((0xffffffff00000000ull & nValue) >> 32) +
           (0x00000000ffffffffull & nValue);
  return nValue;
}
long long pow(long long n, long long m, long long mod = 0) {
  long long ans = 1;
  long long k = n;
  while (m) {
    if (m & 1) {
      ans *= k;
      if (mod) ans %= mod;
    }
    k *= k;
    if (mod) k %= mod;
    m >>= 1;
  }
  return ans;
}
const int maxn = 101000;
struct node {
  int l;
  double p;
  bool operator<(const node &a) const {
    return jud((1 - p) / l / p, (1 - a.p) / a.l / a.p) < 0;
  }
} orig[maxn];
int n;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    int a;
    scanf("%d%d", &orig[i].l, &a);
    orig[i].p = a / 100.0;
  }
  sort(orig, orig + n);
  double ans = 0;
  double temp = 0;
  for (int i = 0; i < n; i++) {
    ans += temp * (1 - orig[i].p) + orig[i].l;
    temp = orig[i].p * (orig[i].l + temp) + temp * (1 - orig[i].p);
  }
  printf("%.10lf\n", ans);
  return 0;
}
