#include <bits/stdc++.h>
using namespace std;
int p[5100];
int t[5100];
double pass[5100];
double dp[5100][5100];
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 0; i < n; i++) {
    cin >> p[i] >> t[i];
  }
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1;
  int sum = 0;
  for (int i = 0; i < n; i++) {
    sum += t[i];
    double calsum = 0;
    if (t[i] == 1) {
      for (int j = 1; j <= T; j++) {
        dp[i + 1][j] = dp[i][j - 1];
      }
    } else {
      double sigma = 0;
      double last = 0;
      double pi = p[i] / 100.0;
      double pii = pow(1 - pi, t[i] - 2);
      int end = min(T, sum);
      for (int j = i + 1; j <= end; j++) {
        dp[i + 1][j] = 0;
        if (j >= t[i]) {
          sigma -= pi * pii * dp[i][j - t[i]];
        }
        sigma *= 1 - pi;
        sigma += pi * dp[i][j - 1];
        if (j >= t[i])
          last = dp[i][j - t[i]] * pii * (1 - pi);
        else
          last = 0;
        dp[i + 1][j] = sigma + last;
      }
    }
    for (int j = 0; j <= T; j++) {
      calsum += dp[i + 1][j];
    }
    pass[i + 1] = calsum;
  }
  double total = 0;
  pass[0] = 1;
  pass[n + 1] = 0;
  for (int i = 1; i <= n + 1; i++) {
    total += (i - 1) * (pass[i - 1] - pass[i]);
  }
  cout << fixed << setprecision(10) << total << endl;
}
