#include <bits/stdc++.h>
using namespace std;
double dp[5001][5001];
int main() {
  cout << setprecision(12) << fixed;
  memset(dp, 0, sizeof(dp));
  int n, T;
  cin >> n >> T;
  int i, j, k, t;
  double p, result = 0, temp, pw;
  dp[0][0] = 1;
  for (i = 0; i < n; i++) {
    cin >> p >> t;
    p /= 100;
    pw = pow(1 - p, t - 1);
    temp = 0.0;
    for (j = 1; j <= T; j++) {
      temp *= 1 - p;
      temp += dp[i][j - 1] * p;
      if (j >= t) temp -= dp[i][j - t] * p * pw;
      dp[i + 1][j] = temp;
      if (j >= t) dp[i + 1][j] += dp[i][j - t] * pw;
      result += dp[i + 1][j];
    }
  }
  cout << result;
  return 0;
}
