#include <bits/stdc++.h>
using namespace std;
const int N = 5e3 + 100;
const int INF = 0x3f3f3f3f;
double f[N][N];
int n, m;
int main() {
  scanf("%d%d", &n, &m);
  f[0][0] = 1;
  double s = 0;
  int x, y;
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &x, &y);
    double p = x / 100.0, q = 0, r = 1, t = 0;
    for (int j = 1; j <= y; j++) q = q + p * r, r = r * (1 - p);
    for (int j = 1; j <= m; j++) {
      t = t * (1 - p) + f[i - 1][j - 1] * p;
      if (j >= y) t = t + f[i - 1][j - y] * (1 - q);
      if (j > y) t = t - f[i - 1][j - y - 1] * r;
      f[i][j] = t;
      s = s + f[i][j];
    }
  }
  printf("%.12lf\n", s);
  return 0;
}
