#include <bits/stdc++.h>
using namespace std;
int t[5050];
double p[5050], dp[5050][5050], a[5050];
int main() {
  int n, m, pp;
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= n; ++i) {
    scanf("%d %d", &pp, &t[i]);
    p[i] = pp / 100.0;
  }
  dp[0][0] = 1;
  p[n + 1] = 0, t[n + 1] = 10000;
  for (int i = 0; i <= n; ++i) {
    int kk = i;
    double tmp = pow(1 - p[i + 1], t[i + 1]);
    for (int j = 0; j <= m; ++j) a[j] = dp[i][j];
    for (int j = 0; j <= m; ++j) {
      dp[i][j + 1] += dp[i][j] * (1 - p[i + 1]);
      dp[i + 1][j + 1] += dp[i][j] * p[i + 1];
      if (t[i + 1] + j <= m) {
        dp[i][j + t[i + 1]] -= a[j] * tmp;
        dp[i + 1][j + t[i + 1]] += a[j] * tmp;
      }
    }
  }
  double ans = 0;
  for (int i = 0; i <= n + 1; ++i) ans += dp[i][m] * i;
  printf("%.6lf\n", ans);
  return 0;
}
