#include <bits/stdc++.h>
using namespace std;
double p[5005], np[5005];
int t[5005];
int n, T;
double dp[5005][5005];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> T;
  for (int i = 0; i < n; i++)
    cin >> p[i] >> t[i], p[i] /= 100, np[i] = 1 - p[i];
  for (int i = n - 1; i >= 0; i--) {
    double middle = 0;
    int done = 0;
    double np_pow_ti_2 = 1;
    for (int j = 1; j <= t[i] - 2; j++) np_pow_ti_2 *= np[i];
    double np_pow_ti_1 = np_pow_ti_2 * np[i];
    for (int j = 1; j <= T; j++) {
      if (t[i] == 1) {
        dp[i][j] = dp[i + 1][j - t[i]] + 1;
        continue;
      }
      middle *= np[i];
      middle += p[i] * (dp[i + 1][j - 1] + 1);
      dp[i][j] += middle;
      done++;
      if (done > t[i] - 2)
        done--, middle -= p[i] * np_pow_ti_2 * (dp[i + 1][j - t[i] + 1] + 1);
      if (j >= t[i]) dp[i][j] += np_pow_ti_1 * (dp[i + 1][j - t[i]] + 1);
    }
  }
  cout << setprecision(15) << fixed << dp[0][T] << "\n";
  return 0;
}
