#include <bits/stdc++.h>
using namespace std;
int n, T;
const int mn = 5009;
double p[mn];
double p2[102][mn];
int pi[mn];
int t[mn];
double dp[2][mn];
int main() {
  scanf("%d", &(n));
  scanf("%d", &(T));
  int pk;
  for (int i = 0; i < n; i++) {
    scanf("%d %d", &pi[i], &t[i]);
    p[i] = pi[i] / 100.0;
  }
  for (int i = 0; i <= 100; i++) {
    p2[i][0] = 1;
    for (int j = 1; j <= T; j++) {
      p2[i][j] = (i / 100.0) * p2[i][j - 1];
    }
  }
  int la = 0;
  double r1 = 0;
  double r2 = 0;
  int i2;
  int i12;
  for (int i = n - 1; i >= 0; i--) {
    la = 0;
    r1 = 0;
    r2 = 0;
    i2 = i % 2;
    i12 = (i + 1) % 2;
    for (int w = 1; w <= T; w++) {
      r1 = (r1) * (1 - p[i]) + dp[i12][w - 1] + 1;
      while (w - la >= t[i]) {
        r1 = r1 - (1 + dp[i12][la]) * p2[100 - pi[i]][t[i] - 1];
        la++;
      }
      r2 = r1 * p[i];
      if (w - t[i] >= 0) {
        r2 = r2 + (dp[i12][w - t[i]] + 1) * p2[100 - pi[i]][t[i] - 1];
      }
      dp[i2][w] = r2;
    }
  }
  printf("%.10lf\n", dp[0][T]);
  return 0;
}
