#include <bits/stdc++.h>
double dp[5001][5001];
int main() {
  dp[0][0] = 1;
  int n, T;
  scanf("%d%d", &n, &T);
  double ans = 0.0;
  int t;
  double p;
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p, &t);
    p = p / 100;
    if (t == 1) {
      for (int j = 1; j <= T; j++) {
        dp[i][j] = dp[i - 1][j - 1];
        ans = ans + dp[i][j];
      }
    } else {
      double pp = pow(1 - p, t - 1);
      double now = dp[i - 1][0], f = 0;
      for (int j = 1; j <= T; j++) {
        dp[i][j] = now * p + f;
        ans = ans + dp[i][j];
        now = now * (1 - p) + dp[i - 1][j];
        if (j >= t - 1) {
          f = pp * dp[i - 1][j - t + 1];
          now = now - f;
        }
      }
    }
  }
  printf("%.9lf\n", ans);
  return 0;
}
