#include <bits/stdc++.h>
int t[5001];
double p[5001], q[5001];
double f[5001][5001];
int main() {
  int N, T;
  int i, j;
  double pro, sum, ans;
  scanf("%d%d", &N, &T);
  for (i = 1; i <= N; ++i) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100, q[i] = 1.0;
    for (j = 1; j < t[i]; ++j) q[i] *= 1 - p[i];
  }
  f[0][0] = 1;
  ans = 0;
  p[N + 1] = 0, t[N + 1] = T;
  for (i = 1; i <= N; ++i) {
    sum = 0;
    for (j = 1; j < t[i]; ++j) {
      sum = sum * (1.0 - p[i]);
      sum += f[i - 1][j - 1] * p[i];
      f[i][j] = sum;
    }
    for (j = t[i]; j <= T; ++j) {
      if (j > t[i]) sum = sum - f[i - 1][j - t[i] - 1] * q[i];
      sum = sum * (1.0 - p[i]) + f[i - 1][j - 1] * p[i] +
            f[i - 1][j - t[i]] * q[i] * (1.0 - p[i]);
      f[i][j] = sum;
    }
    sum = f[i][T], pro = 1 - p[i + 1];
    for (j = 1; j < t[i + 1]; ++j) {
      sum += f[i][T - j] * pro;
      pro *= 1.0 - p[i + 1];
    }
    ans += sum * i;
  }
  printf("%lf", ans);
  return 0;
}
