#include <bits/stdc++.h>
using namespace std;
const int N = 5e3 + 7;
int n, T;
int t[N];
double p[N];
double dp[N], _dp[N];
int main() {
  cin >> n >> T;
  for (int i = (1); i < (n + 1); i++) {
    int a;
    scanf("%d%d", &a, &t[i]);
    p[i] = a / 100.0;
  }
  _dp[0] = 1.0;
  double ans = 0.0;
  for (int i = (1); i < (n + 1); i++) {
    double cut_v = p[i];
    for (int j = (0); j < (t[i]); j++) cut_v *= 1 - p[i];
    double sum = 0.0;
    for (int j = (1); j < (T + 1); j++) {
      sum = sum * (1 - p[i]) + p[i] * _dp[j - 1];
      if (j > t[i]) sum -= _dp[j - t[i] - 1] * cut_v;
      dp[j] = sum;
    }
    double add_v = 1.0;
    for (int j = (0); j < (t[i]); j++) add_v *= 1 - p[i];
    for (int j = (t[i]); j < (T + 1); j++) {
      dp[j] += add_v * _dp[j - t[i]];
    }
    for (int j = (0); j < (i); j++) dp[j] = 0.0;
    for (int j = (0); j < (T + 1); j++) {
      _dp[j] = dp[j];
      ans += dp[j];
    }
  }
  printf("%.15f\n", ans);
  return 0;
}
