#include <bits/stdc++.h>
using namespace std;
int n, tt, t[5050];
double dp[5050][5050], p[5050], powi[5050];
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> tt;
  for (int(i) = 0; (i) < (n); (i)++) cin >> p[i] >> t[i];
  for (int(i) = 0; (i) < (n); (i)++) p[i] /= 100.0;
  for (int(i) = 0; (i) < (n); (i)++) powi[i] = pow(1 - p[i], t[i] - 1);
  for (int(i) = (1); (i) < (tt + 1); (i)++) {
    for (int(j) = 0; (j) < (n); (j)++) {
      if (i < t[j])
        dp[i][j] = (dp[i - 1][j + 1] + 1) * p[j] + dp[i - 1][j] * (1 - p[j]);
      else {
        double val = dp[i - 1][j];
        if (i - 1 >= t[j]) val -= (dp[i - 1 - t[j]][j + 1] + 1.0) * powi[j];
        val *= (1.0 - p[j]);
        val += (dp[i - t[j]][j + 1] + 1.0) * powi[j] * (1 - p[j]);
        val += (dp[i - 1][j + 1] + 1) * p[j];
        dp[i][j] = val;
      }
    }
  }
  cout << setprecision(9) << fixed << dp[tt][0] << "\n";
  return 0;
}
