#include <bits/stdc++.h>
using namespace std;
int n, T;
int t[5005];
double p[5005];
double f[5005][5005];
double res;
double fastpow(double a, int b) {
  if (!b) return 1;
  double res = fastpow(a, b / 2);
  if (b % 2) return res * res * a;
  return res * res;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] = (1 - p[i] / 100.0);
  }
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double pw = fastpow(p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      double s = f[i][j - 1];
      s = f[i][j - 1];
      if (j - 1 >= t[i]) s -= f[i - 1][j - t[i] - 1] * pw;
      s *= p[i];
      if (j >= t[i]) s += f[i - 1][j - t[i]] * pw * p[i];
      s += f[i - 1][j - 1] * (1 - p[i]);
      res += s;
      f[i][j] = s;
    }
  }
  cout << setprecision(10) << fixed << res << '\n';
  return 0;
}
