#include <bits/stdc++.h>
using namespace std;
const int inf = 1 << 30;
const int md = 1e9 + 7;
const int N = 5000 + 5;
double dp[N][N];
double p[N];
int t[N];
int main() {
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1.0;
  int n, T;
  double pp, s, po;
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &pp, &t[i]);
    p[i] = 1.0 - pp / 100.0;
  }
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= T; j++) {
      s = pow(p[i], t[i] - 1);
      po = dp[i][j - 1];
      if (j - 1 >= t[i]) po -= dp[i - 1][j - 1 - t[i]] * s;
      po *= p[i];
      if (j >= t[i]) po += dp[i - 1][j - t[i]] * s * p[i];
      po += dp[i - 1][j - 1] * (1.0 - p[i]);
      dp[i][j] = po;
      ans += dp[i][j];
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
