#include <bits/stdc++.h>
using namespace std;
const int N = 5010;
int n, T;
int t[N];
double p[N];
double dp[N][N];
void initdp() {
  double pw = 1;
  for (int j = 1; j < t[0]; ++j) {
    dp[0][j] = pw * p[0];
    pw *= (1 - p[0]);
  }
  dp[0][t[0]] = pw;
}
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 0; i < n; ++i) {
    scanf("%lf%d", p + i, t + i);
    p[i] /= 100.0;
  }
  initdp();
  double ans = 0;
  for (int i = 1; i < n; ++i) {
    double old = 0;
    int oldl = 0, oldr = -1;
    double tmp = pow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; ++j) {
      old *= (1 - p[i]);
      if (j - oldl == t[i]) {
        old -= dp[i - 1][oldl] * tmp;
        oldl++;
      }
      oldr++;
      old += dp[i - 1][oldr];
      dp[i][j] = old * p[i];
      int ps = j - t[i];
      if (ps >= 0) {
        dp[i][j] += dp[i - 1][ps] * tmp;
      }
    }
  }
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j <= T; ++j) {
      ans += dp[i][j];
    }
  }
  printf("%.12f\n", ans);
  return 0;
}
