#include <bits/stdc++.h>
using namespace std;
int n, T;
double p[100001];
int t[100001];
double ans = 0.00;
double s[5001][5001];
double k[6000];
void dp() {
  s[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    k[0] = 1.0;
    for (int j = 1; j <= T; j++) {
      k[j] = k[j - 1] * (1 - p[i]);
    }
    double sum = 0.0;
    for (int j = 1; j <= T; j++) {
      if (j - 1 >= t[i] - 1 && t[i] - 1 >= 1) {
        sum -= s[i - 1][j - t[i]] * k[t[i] - 2];
      }
      sum *= k[1];
      if (t[i] - 1 >= 1) {
        sum += s[i - 1][j - 1];
      }
      s[i][j] += (j >= t[i] ? s[i - 1][j - t[i]] * k[t[i] - 1] : 0.0);
      s[i][j] += sum * p[i];
    }
  }
}
int main() {
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    int a, b;
    scanf("%d %d", &a, &b);
    p[i] = a;
    t[i] = b;
    p[i] /= 100.00;
  }
  dp();
  double ans = 0.0;
  for (int i = 0; i <= n; i++) {
    for (int j = 1; j <= T; j++) {
      ans += s[i][j];
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
