#include <bits/stdc++.h>
using namespace std;
int n, T, t[5005];
double res = 0, p[5005], f[5005][5005], g[5005];
double pow(double a, int n) {
  double res = 1;
  while (n) {
    if (n & 1) res *= a;
    a *= a;
    n >>= 1;
  }
  return res;
}
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  f[1][1] = 1;
  t[n + 1] = 5000;
  for (int i = 1; i <= n + 1; i++) {
    double tmp = pow(1 - p[i], t[i]);
    for (int j = 1; j <= T + 1; j++) g[j] = f[i][j];
    for (int j = 1; j <= T + 1; 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] * tmp, f[i + 1][j + t[i]] += g[j] * tmp;
    }
  }
  for (int i = 1; i <= n + 1; i++) res += f[i][T + 1] * (i - 1);
  printf("%lf\n", res);
  return 0;
}
