#include <bits/stdc++.h>
using namespace std;
double p[5005], f[5005][5005], ans;
int n, T, x, t[5005];
double Pow(double a, int b) {
  double rec = 1;
  for (; b; b >>= 1, a = a * a)
    if (b & 1) rec = rec * a;
  return rec;
}
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1, x; i <= n; i++) {
    scanf("%d%d", &x, &t[i]);
    p[i] = 1.0 * x / 100.0;
  }
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double sum = 0, la = Pow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      sum *= 1 - p[i];
      sum += f[i - 1][j - 1] * p[i];
      if (j >= t[i]) {
        sum -= f[i - 1][j - t[i]] * la * p[i];
        f[i][j] += f[i - 1][j - t[i]] * la;
      }
      f[i][j] += sum;
      ans += f[i][j];
    }
  }
  printf("%.9lf\n", ans);
}
