#include <bits/stdc++.h>
using namespace std;
const int NMAX = 5e3;
const double eps = 1e-14;
double dp[NMAX + 5][NMAX + 5];
int n, k;
double p[NMAX + 5];
double np[NMAX + 5];
int t[NMAX + 5];
int main() {
  scanf("%d %d", &n, &k);
  for (int i = 1; i <= n; i++) {
    int x;
    scanf("%d %d", &x, &t[i]);
    p[i] = x / 100.0;
    np[i] = (100 - x) / 100.0;
  }
  dp[0][0] = 1;
  for (int i = 0; i <= n; i++) {
    double prob = 1;
    for (int j = 1; j <= t[i + 1]; j++) {
      prob *= np[i + 1];
    }
    for (int j = i; j <= k; j++) {
      if (dp[i][j] < eps) {
        continue;
      }
      if (j < k) {
        dp[i][j + 1] += dp[i][j] * np[i];
        dp[i + 1][j + 1] += dp[i][j] * p[i + 1];
        if (j <= k - t[i + 1]) {
          dp[i + 1][j + t[i + 1]] += dp[i][j] * prob;
          if (j <= k - t[i + 1] - 1) {
            dp[i + 1][j + t[i + 1] + 1] -= dp[i][j] * prob;
          }
        }
      }
    }
  }
  double ans = 0;
  for (int i = 1; i < n; i++) {
    double prob = 1;
    for (int j = k; j > k - t[i + 1]; j--) {
      ans += i * dp[i][j] * prob;
      prob *= (1 - p[i + 1]);
    }
  }
  for (int j = 1; j <= k; j++) {
    ans += n * dp[n][j];
  }
  printf("%.9f\n", ans);
  return 0;
}
