#include <bits/stdc++.h>
using namespace std;
double p[5007];
int t[5007];
double totalMul[5007];
double mp[5007][5007];
double prob[5007];
int main() {
  int N, T;
  scanf("%d %d ", &N, &T);
  ;
  for (int i = (0); i < (N); i++) {
    cin >> p[i] >> t[i];
    p[i] *= 0.01;
    totalMul[i] = 1;
    int r = t[i] - 1;
    int msk = 1;
    double mul = 1.0 - p[i];
    while (r) {
      if (r & msk) {
        totalMul[i] *= mul;
        r -= msk;
      }
      msk <<= 1;
      mul *= mul;
    }
  }
  mp[0][0] = 1;
  prob[0] = 1;
  for (int ti = (1); ti < (T + 1); ti++) {
    for (int i = (N - 1); i >= (0); i--) {
      double diff = 0;
      if (ti - t[i] >= 0) diff = mp[i][ti - t[i]] * totalMul[i];
      mp[i + 1][ti] += diff;
      prob[i + 1] += diff;
      prob[i] -= diff;
      diff = prob[i] * p[i];
      mp[i + 1][ti] += diff;
      prob[i + 1] += diff;
      prob[i] -= diff;
    }
  }
  double res = 0;
  for (int i = (0); i < (N + 1); i++) {
    res += prob[i] * (double)i;
  }
  printf("%.9lf\n", res);
  return 0;
}
