#include <bits/stdc++.h>
const int MAXN = 5000 + 10;
int n, t;
int p[MAXN], l[MAXN];
namespace solver1 {
double f[MAXN][MAXN];
double p[MAXN];
void main() {
  f[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    p[i] = 1.0 * ::p[i] / 100;
  }
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double k = f[i - 1][0] * p[i];
    double q = pow(1 - p[i], l[i] - 1);
    double qq = pow(1 - p[i], l[i] - 2) * p[i];
    for (int j = 1; j <= t; j++) {
      if (l[i] == 1) {
        f[i][j] = f[i - 1][j - 1];
      } else {
        f[i][j] += k;
        if (j - l[i] >= 0) {
          f[i][j] += f[i - 1][j - l[i]] * q;
        }
        if (j - l[i] + 1 >= 0) {
          k -= f[i - 1][j - l[i] + 1] * qq;
        }
        k *= 1 - p[i];
        k += f[i - 1][j] * p[i];
      }
      ans += f[i][j];
    }
  }
  printf("%.12lf\n", ans);
}
}  // namespace solver1
int main() {
  scanf("%d%d", &n, &t);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", p + i, l + i);
  }
  solver1::main();
}
