#include <bits/stdc++.h>
using namespace std;
const bool DEBUG_FLAG = 0;
int GetInt() {
  register int aa = 0, bb = 1;
  register char ch = getchar();
  while ((ch < '0' || ch > '9') && ch != '-') ch = getchar();
  ch == '-' ? aa = 0, bb = -1 : aa = ch - '0';
  while (ch = getchar(), ch >= '0' && ch <= '9')
    aa = (aa << 1) + (aa << 3) + ch - '0';
  return bb == 1 ? aa : -aa;
}
const int N = 5010;
int n, T, t[N];
double p[N], f[N][N];
int main() {
  register int i, j;
  register double Ans = 0;
  n = GetInt();
  T = GetInt();
  for (i = 0; i < n; i++) {
    p[i] = GetInt() * 0.01;
    t[i] = GetInt();
  }
  t[n] = N;
  f[0][0] = 1;
  for (i = 0; i <= n; i++) {
    register double P = pow(1 - p[i], t[i]);
    for (j = T; j >= 0; j--) {
      if (j + t[i] <= T) {
        f[i][j + t[i]] -= f[i][j] * P;
        f[i + 1][j + t[i]] += f[i][j] * P;
      }
    }
    for (j = 0; j < T; j++) {
      f[i][j + 1] += f[i][j] * (1 - p[i]);
      f[i + 1][j + 1] += f[i][j] * p[i];
    }
  }
  for (i = 1; i <= n; i++) {
    Ans += f[i][T] * i;
  }
  printf("%.8lf", Ans);
}
