#include <bits/stdc++.h>
using namespace std;
bool debug = false;
double dp[5005][5005];
int n, T;
double qp(double a, int b) {
  if (b == 0) {
    return 1;
  }
  double ans = qp(a, b / 2);
  if (b % 2) {
    return ans * ans * a;
  } else {
    return ans * ans;
  }
}
int main(int argc, char* argv[]) {
  ios::sync_with_stdio(0);
  cin >> n >> T;
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 0; i < n; i++) {
    int a, b;
    cin >> a >> b;
    double p = a * 0.01;
    double r1 = qp(1 - p, b - 1);
    double r2 = r1;
    r1 *= p;
    double now = 0;
    for (int j = 0; j <= T; j++) {
      now *= (1 - p);
      now += p * dp[i][j];
      if (j + 1 >= b) {
        now -= r1 * dp[i][j + 1 - b];
        dp[i + 1][j + 1] = now + dp[i][j + 1 - b] * r2;
      } else {
        dp[i + 1][j + 1] = now;
      }
    }
    for (int j = 0; j <= T; j++) {
      ans += dp[i + 1][j];
    }
  }
  printf("%f", ans);
  return 0;
}
