#include <bits/stdc++.h>
using namespace std;
double dp[5002][5002] = {{0}};
int x[5002];
double p[5002];
int main() {
  int n, t;
  cin >> n >> t;
  for (int i = 1; i <= n; i++) {
    double p_;
    cin >> p_;
    p[i] = p_ / 100;
    cin >> x[i];
  }
  dp[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    double pre = dp[i - 1][0];
    for (int j = 1; j <= t; ++j) {
      dp[i][j] = p[i] * pre;
      pre = pre * (1 - p[i]) + dp[i - 1][j];
      if (j >= x[i]) {
        pre -= dp[i - 1][j - x[i]] * pow(1 - p[i], x[i]);
        dp[i][j] += dp[i - 1][j - x[i]] * pow(1 - p[i], x[i]);
      }
    }
  }
  double res = 0;
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= t; ++j) {
      res += dp[i][j];
    }
  }
  cout << fixed << setprecision(10) << res << endl;
  return 0;
}
