#include <bits/stdc++.h>
double f[5000 + 5][5000 + 5];
int p[5000 + 5], t[5000 + 5];
double ksm(double x, int y) {
  double ans = 1.0;
  for (int i = 0; i < y; i++) {
    ans *= x;
  }
  return ans;
}
int main() {
  int n, T;
  scanf("%d%d", &n, &T);
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &p[i], &t[i]);
  }
  double ans = 0.0, pp;
  double r_1, r_2, now;
  f[0][0] = 1.0;
  for (int i = 0; i < n; i++) {
    pp = p[i] / 100.0;
    now = 0.0;
    r_2 = ksm(1 - pp, t[i] - 1);
    r_1 = r_2 * pp;
    for (int j = 0; j < T; j++) {
      now += (f[i][j] - now) * pp;
      if (j + 1 >= t[i]) {
        now -= f[i][j + 1 - t[i]] * r_1;
        f[i + 1][j + 1] += now + f[i][j + 1 - t[i]] * r_2;
      } else {
        f[i + 1][j + 1] += now;
      }
    }
    for (int j = 0; j <= T; j++) {
      ans += f[i + 1][j];
    }
  }
  printf("%.9lf\n", ans);
  return 0;
}
