#include <bits/stdc++.h>
using namespace std;
const int N = 5011;
double dp[N][N];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  double ret = 0;
  double p, q, temp;
  int n;
  int t;
  int T;
  cin >> n >> T;
  dp[0][0] = 1;
  for (int i = 0; i < n; i += 1) {
    temp = 0;
    cin >> p >> t;
    p /= 100;
    q = pow(1 - p, t - 1);
    for (int j = 1; j <= T; j += 1) {
      temp *= (1 - p);
      temp += dp[i][j - 1] * p;
      if (j >= t) {
        temp -= dp[i][j - t] * p * q;
      }
      dp[i + 1][j] = temp;
      if (j >= t) {
        dp[i + 1][j] += dp[i][j - t] * q;
      }
      ret += dp[i + 1][j];
    }
  }
  printf("%0.9lf\n", ret);
  return 0;
}
