#include <bits/stdc++.h>
double p[5005];
int t[5005];
double prob[5005][5005];
int N, T;
int main() {
  scanf("%d%d", &N, &T);
  for (int i = 0; i < N; ++i) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] *= 0.01;
  }
  prob[0][0] = 1;
  double ans = 0;
  double cur = 0;
  double tmp = 0;
  double q;
  for (int i = 1; i <= N; ++i) {
    cur = 0;
    tmp = 0;
    q = pow(1 - p[i - 1], t[i - 1] - 1);
    for (int k = 0; k <= T; ++k) {
      cur = cur * (1 - p[i - 1]) + prob[i - 1][k];
      if (k >= t[i - 1] - 1) {
        cur -= prob[i - 1][k - t[i - 1] + 1] * q;
        prob[i][k] += prob[i - 1][k - t[i - 1]] * q;
      }
      if (k >= T - t[i - 1] && k < T) {
        tmp = prob[i - 1][k + 1] + (1 - p[i - 1]) * tmp;
      }
      prob[i][k + 1] = cur * p[i - 1];
    }
    ans += tmp * (i - 1);
  }
  for (int k = 0; k <= T; ++k) {
    ans += N * prob[N][k];
  }
  printf("%.12lf\n", ans);
  return 0;
}
