#include <bits/stdc++.h>
using namespace std;
const int maxN = 5005;
const int oo = (1 << 30) - 10;
int n, T;
double p[maxN];
int t[maxN];
double f[maxN][maxN];
double g[maxN];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; ++i) {
    int x;
    scanf("%d%d", &x, &t[i]);
    p[i] = 1.0 * x / (1.0 * 100);
  }
  f[1][1] = 1;
  for (int i = 1; i <= n + 1; ++i) {
    for (int j = 0; j <= T; ++j) g[j] = f[i][j];
    double pp = pow(1 - p[i], t[i]);
    if (i == 0) pp = 0;
    for (int j = 0; j <= T; ++j)
      if (f[i][j]) {
        f[i][j + 1] += f[i][j] * (1 - p[i]);
        f[i + 1][j + 1] += f[i][j] * p[i];
        if (j + t[i] <= T + 1) {
          f[i][j + t[i]] -= g[j] * pp;
          f[i + 1][j + t[i]] += g[j] * pp;
        }
      }
  }
  double ans = 0;
  for (int i = 2; i <= n + 1; ++i) ans += f[i][T + 1] * (i - 1);
  ans = ans;
  printf("%.9lf\n", ans);
  return 0;
}
