#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 5e3 + 10;
int n, T;
double p[MAXN];
int t[MAXN];
double ans = 0;
double dp[MAXN][MAXN];
inline double super_pow(double num, int now) {
  if (num == 0) return 0;
  if (now == 0) return 1;
  if (now == 1) return num;
  if (now & 1) {
    return super_pow(num, now / 2) * super_pow(num, now / 2) * num;
  } else
    return super_pow(num, now / 2) * super_pow(num, now / 2);
}
void work() {
  for (int i = 1; i <= n; i++) {
    double NOW = 0;
    double R = super_pow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      if (j - t[i] < 0)
        dp[i][j] = 0;
      else
        dp[i][j] = dp[i - 1][j - t[i]] * R;
      double SQUARE = 1.0;
      if (j > t[i] - 1) {
        double minus_num = dp[i - 1][j - t[i]] * R * p[i];
        if ((1.0 - p[i])) minus_num /= (1.0 - p[i]);
        NOW -= minus_num;
      }
      NOW *= (1.0 - p[i]);
      NOW += dp[i - 1][j - 1] * p[i];
      dp[i][j] += NOW;
      ans += dp[i][j];
    }
  }
}
int main() {
  memset(dp, 0, sizeof(dp));
  ios::sync_with_stdio(false);
  cin >> n;
  ;
  cin >> T;
  ;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100.0;
  }
  dp[0][0] = 1;
  work();
  printf("%.12f", ans);
  return 0;
}
