#include <bits/stdc++.h>
using namespace std;
double dp[5002][5002], gqk[102][5002];
double res = (double)0.0;
int n, T, t[5002], p[5002], sum;
int main() {
  dp[0][0] = (double)1.0;
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &p[i], &t[i]);
  }
  for (int i = 0; i <= 100; i++) {
    gqk[i][0] = (double)1.0;
    for (int j = 1; j < 5001; j++) {
      gqk[i][j] = (double)((double)gqk[i][j - 1] * (double)((double)(i) / 100));
    }
  }
  for (int i = 1; i <= n; i++) {
    sum += t[i];
    double ga = (double)0.0;
    for (int j = i; j <= T; j++) {
      ga = (double)(ga * (double)((double)(100 - p[i]) / 100) +
                    (double)dp[i - 1][j - 1]);
      if (j >= t[i]) {
        ga -= dp[i - 1][j - t[i]] * gqk[100 - p[i]][t[i] - 1];
        dp[i][j] = (double)ga * p[i] / 100 +
                   dp[i - 1][j - t[i]] * gqk[100 - p[i]][t[i] - 1];
      } else {
        dp[i][j] = (double)ga * p[i] / 100;
      }
      res += dp[i][j];
    }
  }
  cout << fixed << setprecision(9) << (double)(res) << endl;
  return 0;
}
