#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5010;
int n, T;
double dp[MAXN + 1][MAXN + 1];
int main() {
  cout << setprecision(12) << fixed;
  while (cin >> n >> T) {
    memset(dp, 0, sizeof(dp));
    dp[0][0] = 1;
    double ans = 0;
    for (int i = (0); i < (n); i++) {
      int t;
      double p;
      cin >> p >> t;
      p /= 100;
      double r = 0;
      double q = pow(1 - p, t - 1);
      for (int j = 1; j <= T; j++) {
        r *= 1 - p;
        if (j >= t) r -= dp[i][j - t] * p * q;
        r += dp[i][j - 1] * p;
        dp[i + 1][j] = r;
        if (j >= t) dp[i + 1][j] += q * dp[i][j - t];
        ans += dp[i + 1][j];
      }
    }
    cout << ans << endl;
  }
  return 0;
}
