#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 5500;
int n, T;
double p[MAX_N];
int t[MAX_N];
double dq[MAX_N];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 0; i < n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  vector<double> cur(T + 1), nxt(T + 1);
  double exp = 0;
  cur[0] = 1;
  for (int i = 0; i < n; i++) {
    double prb = 0;
    double f = 1.0;
    int s1 = 0, s2 = 0;
    for (int j = 0; j < t[i] - 1; j++) {
      f *= 1.0 - p[i];
    }
    for (int j = 0; j <= T; j++) {
      double poped = 0;
      if (s2 - s1 > t[i] - 1) {
        poped = dq[s1];
        prb -= f * dq[s1];
        s1++;
      }
      nxt[j] = f * poped + prb * p[i];
      dq[s2] = cur[j];
      s2++;
      prb = (1.0 - p[i]) * prb + cur[j];
    }
    exp += i * prb;
    cur.swap(nxt);
    fill(nxt.begin(), nxt.end(), 0);
  }
  printf("%.15f\n", exp + n * accumulate(cur.begin(), cur.end(), 0.0));
}
