#include <bits/stdc++.h>
using namespace std;
double dp[5010][5010];
int n, T;
double p[5050];
int t[5050];
double finP[5050];
int main() {
  int i, j, k;
  scanf("%d %d", &n, &T);
  for (i = 0; i < n; i++) {
    scanf("%lf %d", &p[i], &t[i]);
    p[i] /= 100;
  }
  for (i = 0; i <= 0; i++) {
    double pr = p[i];
    double sum = 1;
    for (j = 1; j <= t[i]; j++) {
      if (j >= t[i]) {
        dp[i][j] = sum;
      } else {
        dp[i][j] = sum * pr;
      }
      sum *= (1 - pr);
    }
  }
  for (i = 1; i < n; i++) {
    double pr = (p[i]);
    double tp = 1;
    for (j = 0; j < t[i]; j++) tp *= (1 - pr);
    double tp1 = 1;
    for (j = 1; j < t[i]; j++) tp1 *= (1 - pr);
    double sum = 0;
    for (j = 1; j <= T; j++) {
      sum *= (1 - pr);
      sum += dp[i - 1][j - 1] * pr;
      if (j >= t[i]) {
        if (j > t[i]) sum -= tp * dp[i - 1][j - 1 - t[i]];
        sum -= tp1 * pr * dp[i - 1][j - t[i]];
        sum += tp1 * dp[i - 1][j - t[i]];
      }
      dp[i][j] = sum;
    }
  }
  for (i = 0; i < (n - 1); i++) {
    double sum = 0;
    double mult = 1;
    for (j = T; j > (T - t[i + 1]); j--) {
      sum += mult * dp[i][j];
      mult *= (1 - p[i + 1]);
    }
    finP[i] = sum;
  }
  for (i = n - 1; i <= (n - 1); i++) {
    double sum = 0;
    for (j = T; j >= 0; j--) {
      sum += dp[i][j];
    }
    finP[i] = sum;
  }
  double sum = 0;
  for (i = 0; i < n; i++) {
    sum += (i + 1) * finP[i];
  }
  printf("%.12lf\n", sum);
  return 0;
}
