#include <bits/stdc++.h>
using namespace std;
int n;
struct aaa {
  int l, p;
} a[50001];
double pr(int x) { return (double)x / 100.0; }
bool cmp(const aaa a, const aaa b) {
  return a.l * a.p * 0.01 - a.l * a.p * 0.01 * b.p * 0.01 >
         b.l * b.p * 0.01 - b.l * a.p * 0.01 * b.p * 0.01;
}
double f[500001][2];
double x[500001];
int main(int argc, char *argv[]) {
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    scanf("%d%d", &a[i].l, &a[i].p);
  }
  sort(a, a + n, cmp);
  x[0] = a[0].l * pr(a[0].p);
  for (int i = 1; i < n; ++i) {
    x[i] += x[i - 1] + a[i].l * pr(a[i].p);
  }
  f[0][0] = a[0].l;
  f[0][1] = a[0].l;
  for (int i = 1; i < n; ++i) {
    double xx =
        f[i - 1][0] * pr(a[i - 1].p) + f[i - 1][1] * (1 - pr(a[i - 1].p));
    f[i][0] = xx + a[i].l;
    f[i][1] = x[i - 1] + xx + a[i].l;
  }
  printf("%f\n",
         f[n - 1][0] * pr(a[n - 1].p) + f[n - 1][1] * (1 - pr(a[n - 1].p)));
  return 0;
}
