#include <bits/stdc++.h>
using namespace std;
double dp[5005][5005], temp[5005], P[5005];
int ttt[5005];
int main() {
  int n, T, i, j;
  scanf("%d", &n);
  scanf("%d", &T);
  for (i = n - 1; i >= 0; i--) {
    int pr;
    scanf("%d", &pr);
    scanf("%d", &ttt[i]);
    P[i] = (double)pr / 100.0;
  }
  dp[0][0] = 0;
  for (i = 1; i < 5005; i++) {
    if (i >= ttt[0])
      dp[0][i] = 1;
    else
      dp[0][i] = P[0] + (1.0 - P[0]) * dp[0][i - 1];
  }
  double pr, revpr, p;
  int t;
  for (i = 1; i < n; i++) {
    pr = P[i];
    revpr = 1.0 - pr;
    temp[0] = pr;
    t = ttt[i];
    p = 1;
    for (j = 1; j < t; j++) p *= revpr;
    for (j = 1; j < 5005; j++) {
      dp[i][j] = temp[j - 1];
      if (j >= t) {
        dp[i][j] -= (temp[j - t] * p);
        dp[i][j] += (p * (1 + dp[i - 1][j - t]));
      }
      temp[j] = temp[j - 1] * revpr;
      temp[j] += (pr * (1 + dp[i - 1][j]));
    }
  }
  cout << fixed << setprecision(15);
  cout << dp[n - 1][T] << endl;
  return 0;
}
