#include <bits/stdc++.h>
using namespace std;
double pi[5000];
int ti[5000], N, Tt;
double dp[5001][5001];
int main() {
  cin >> N >> Tt;
  for (int n = 0; n < N; n++) {
    cin >> pi[n] >> ti[n];
    pi[n] *= 0.01;
  }
  for (int n = N - 1; n >= 0; n--) {
    double ans = 0.0, rp = pi[n], cache[5001] = {};
    for (int T = 1; T <= Tt; T++) {
      double np = (T > 1 && n != N - 1) ? dp[T - 1][n + 1] : 0;
      ans = (1.0 - rp) * ans + rp * (1 + np);
      cache[T] = dp[T][n] = ans;
      if (T >= ti[n]) {
        np = (T - ti[n] >= 1 && n != N - 1) ? dp[T - ti[n]][n + 1] : 0;
        dp[T][n] += pow(1.0 - rp, ti[n]) * ((1 + np) - cache[T - ti[n]]);
      }
    }
  }
  cout << fixed << setprecision(10) << dp[Tt][0] << endl;
}
