#include <bits/stdc++.h>
using namespace std;
double DP[5010][5010];
double probs[5010];
int ch[5010];
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 0; i < n; i++) {
    cin >> probs[i] >> ch[i];
    probs[i] /= 100;
  }
  probs[n] = 0;
  ch[n] = T + 1;
  memset(DP, 0, sizeof(DP));
  DP[0][0] = 1;
  for (int i = 0; i < n; i++) {
    double prob = 0;
    double rest = 1;
    for (int j = 0; j < ch[i] - 1; j++) rest *= (1.0 - probs[i]);
    for (int j = 0; j < T; j++) {
      prob *= (1.0 - probs[i]);
      prob += probs[i] * DP[i][j];
      DP[i + 1][j + 1] += prob;
      if (j + 1 >= ch[i])
        DP[i + 1][j + 1] += rest * (1.0 - probs[i]) * DP[i][j - ch[i] + 1];
      if (j + 1 >= ch[i]) prob -= rest * probs[i] * DP[i][j - ch[i] + 1];
    }
  }
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double prob = 1;
    for (int j = 0; j < (int)(min(ch[i], T + 1)); ++j) {
      ans += prob * i * (DP[i][T - j]);
      prob *= (1.0 - probs[i]);
    }
  }
  printf("%.7f\n", ans);
  return 0;
}
