#include <bits/stdc++.h>
using namespace std;
using namespace std;
int n, T;
int t[5005];
double p[5005];
double dp[5005][5005];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> T;
  for (int i = 1; i <= n; i++) cin >> p[i] >> t[i], p[i] *= 0.01;
  dp[0][0] = 1;
  double ex = 0;
  for (int i = 1; i <= n; i++) {
    double r = 1.0;
    for (int j = 0; j < t[i]; j++) r *= (1.0 - p[i]);
    double sum = 0;
    for (int j = 1; j <= T; j++) {
      sum = sum * (1.0 - p[i]) + dp[i - 1][j - 1];
      if (j > t[i]) sum = sum - r * dp[i - 1][j - t[i] - 1];
      dp[i][j] = sum * p[i];
      if (j >= t[i]) dp[i][j] += r * dp[i - 1][j - t[i]];
      ex += dp[i][j];
    }
  }
  cout << setprecision(13) << fixed << ex;
}
