#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, T;
  cin >> N >> T;
  double p[N];
  int t[N];
  for (int i = 0; i < N; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100.0;
  }
  double dp[N + 1][T + 1];
  double pow[N];
  for (int i = 0; i < N; i++) {
    pow[i] = 1;
    for (int j = 0; j < t[i]; j++) {
      pow[i] *= (1 - p[i]);
      if (pow[i] < 0.00000000000001) {
        pow[i] = 0;
        break;
      }
    }
  }
  dp[0][0] = 1;
  for (int i = 1; i <= T; i++) dp[0][i] = 0;
  for (int i = 1; i <= N; i++) dp[i][0] = 0;
  for (int i = 1; i <= N; i++)
    for (int j = 1; j <= T; j++) {
      dp[i][j] = dp[i][j - 1] * (1 - p[i - 1]) + dp[i - 1][j - 1] * p[i - 1];
      if (j >= t[i - 1]) dp[i][j] += dp[i - 1][j - t[i - 1]] * pow[i - 1];
      if (j > t[i - 1]) dp[i][j] -= dp[i - 1][j - t[i - 1] - 1] * pow[i - 1];
      if (dp[i][j] < 0.00000000000001) dp[i][j] = 0;
    }
  double ans = 0;
  for (int i = 0; i <= N; i++) {
    double pp = 0;
    if (i == N) {
      for (int j = 0; j <= T; j++) pp += dp[i][j];
    } else {
      double tmp = 1;
      for (int j = 0; j <= T && j < t[i]; j++) {
        pp += dp[i][T - j] * tmp;
        tmp *= 1 - p[i];
        if (tmp < 0.00000000000001) break;
      }
    }
    ans += i * pp;
  }
  cout << setprecision(10) << fixed << ans << endl;
}
