#include <bits/stdc++.h>
using namespace std;
int n, T;
double p[5555];
int t[5555];
double f[5555][5555];
int main() {
  cin >> n >> T;
  for (int i = 0; i < n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100;
  }
  for (int x = 1; x < t[n - 1]; x++)
    f[n - 1][x] = f[n - 1][x - 1] + p[n - 1] * pow(1 - p[n - 1], x - 1);
  f[n - 1][t[n - 1]] = f[n - 1][t[n - 1] - 1] + pow(1 - p[n - 1], t[n - 1] - 1);
  for (int x = t[n - 1] + 1; x <= T; x++) f[n - 1][x] = 1;
  for (int i = n - 2; i >= 0; i--) {
    double s = 0;
    for (int x = 1; x <= T; x++) {
      s *= (1 - p[i]);
      s += (f[i + 1][x - 1] + 1) * p[i];
      if (x >= t[i])
        s -= (f[i + 1][x - t[i]] + 1) * p[i] * pow(1 - p[i], t[i] - 1);
      if (x >= t[i])
        f[i][x] = s + (f[i + 1][x - t[i]] + 1) * pow(1 - p[i], t[i] - 1);
      else
        f[i][x] = s;
    }
  }
  cout << setprecision(15) << f[0][T] << '\n';
  return 0;
}
