#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:60777216")
using namespace std;
int n, T;
double x[5055][5055];
int main() {
  cin >> n >> T;
  x[0][0] = 1;
  int p, t;
  double res = 0;
  for (int i = (0); i < (n); i++) {
    cin >> p >> t;
    double pr = p / 100.;
    double ipr = 1 - pr;
    double guess = pow(ipr, t);
    double* x1 = x[i];
    double* x2 = x[i + 1];
    double sum = 0;
    for (int j = 0; j <= T; j++) {
      x2[j] = sum * pr;
      sum = sum * ipr + (j < T ? x1[j] : 0.);
      if (j - t >= 0) {
        sum -= x1[j - t] * guess;
        x2[j] += x1[j - t] * guess;
      }
    }
    res += sum * i;
  }
  for (int i = (0); i < (n + 1); i++) {
    res += x[i][T] * i;
  }
  for (int i = (0); i < (T); i++) {
    res += n * x[n][i];
  }
  printf("%.10lf\n", res);
  return 0;
}
