#include <bits/stdc++.h>
const long long INF = 1e9;
const long long lINF = 1e18;
const double EPS = 1e-12;
using namespace std;
int n, T;
double prob[5555][5555], ans;
int main() {
  scanf("%d%d", &n, &T);
  prob[0][0] = 1;
  int t[5555];
  double p[5555], sum = 0, sum2 = 0;
  for (int i = 0; i < n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  for (int i = 0; i < n; i++) {
    sum = 0;
    sum2 = 0;
    double pow2 = 1, pp = 1 - p[i];
    for (int j = 0; j < t[i] - 1; j++) {
      pow2 *= pp;
      if (pow2 < EPS) {
        pow2 = 0;
      }
    }
    for (int j = i + 1; j < t[i]; j++) {
      sum2 *= pp;
      if (sum2 < EPS) {
        sum2 = 0;
      }
      sum2 += p[i] * prob[i][j - 1];
      prob[i + 1][j] = sum2;
      ans += prob[i + 1][j];
    }
    for (int j = max(t[i], i + 1); j <= T; j++) {
      sum2 *= pp;
      if (sum2 < EPS) {
        sum2 = 0;
      }
      sum2 += p[i] * (prob[i][j - 1] - prob[i][j - t[i]] * pow2);
      prob[i + 1][j] = prob[i][j - t[i]] * pow2 + sum2;
      ans += prob[i + 1][j];
    }
  }
  printf("%.10f", ans);
  return 0;
}
