#include <bits/stdc++.h>
const long long INF = 1e9;
const long long lINF = 1e18;
using namespace std;
int n, T;
double prob[5555], ans, prob2[5555];
int main() {
  cin >> n >> T;
  prob[0] = 1;
  for (int i = 0; i < n; i++) {
    int t;
    double p;
    double sum = 0, sum2 = 0;
    scanf("%lf%d", &p, &t);
    p /= 100;
    double pow2 = pow(1 - p, t - 1);
    for (int j = 1; j <= T; j++) {
      sum2 *= (1 - p);
      sum2 += p * prob[j - 1];
      prob2[j] = 0;
      if (j - t >= 0 && t > 0) {
        sum2 -= p * prob[j - t] * pow2;
        prob2[j] += prob[j - t] * pow2;
      }
      prob2[j] += sum2;
    }
    for (int j = 0; j <= T; j++) {
      prob[j] = prob2[j];
      sum += prob[j];
    }
    ans += sum;
  }
  printf("%.10f", ans);
  return 0;
}
