#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5005;
int N, T, ch[MAXN];
double pr[MAXN];
double dp[MAXN][MAXN];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> N >> T;
  for (int i = 0; i < N; i++) {
    cin >> pr[i] >> ch[i];
    pr[i] /= 100;
  }
  for (int s = N - 1; s >= 0; s--) {
    double sf = 0;
    double pw = pow(1 - pr[s], ch[s]);
    for (int t = 1; t <= T; t++) {
      sf *= (1 - pr[s]);
      if (t > ch[s]) sf -= pw * pr[s] * (1 + dp[s + 1][t - ch[s] - 1]);
      sf += pr[s] * (1 + dp[s + 1][t - 1]);
      dp[s][t] = sf;
      if (t >= ch[s]) dp[s][t] += pw * (1 + dp[s + 1][t - ch[s]]);
    }
  }
  cout.precision(20);
  cout << dp[0][T] << endl;
  return 0;
}
