#include <bits/stdc++.h>
using namespace std;
int n, T, t[5100];
double p[5100], f[5100][5100];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  f[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double sum = 0, tmp = 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]] * tmp * p[i];
        f[i][j] += f[i - 1][j - t[i]] * tmp;
      }
      f[i][j] += sum;
      ans += f[i][j];
    }
  }
  printf("%.12lf\n", ans);
  return 0;
}
