#include <bits/stdc++.h>
const int N = 5005;
int n, T, t[N];
double p[N], f[N][N], ans;
int read() {
  int x = 0, f = 1;
  char s;
  while ((s = getchar()) < '0' || s > '9')
    if (s == '-') f = -1;
  while (s >= '0' && s <= '9') {
    x = (x << 1) + (x << 3) + (s ^ 48);
    s = getchar();
  }
  return x * f;
}
double qkpow(double x, int y) {
  double r = 1;
  while (y) {
    if (y & 1) r *= x;
    x *= x;
    y >>= 1;
  }
  return r;
}
int main() {
  n = read(), T = read();
  for (int i = 1; i <= n; ++i) p[i] = 1.0 * read() / 100, t[i] = read();
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    double sum = 0, w = qkpow(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]] * w * p[i];
        f[i][j] += f[i - 1][j - t[i]] * w;
      }
      f[i][j] += sum;
      ans += f[i][j];
    }
  }
  printf("%.9f\n", ans);
  return 0;
}
