#include <bits/stdc++.h>
using namespace std;
const int N = 5010;
double dp[N][N];
const double eps = 1e-9;
int main() {
  int n, T, t;
  scanf("%d%d", &n, &T);
  double p;
  double ans = 0;
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p, &t);
    p = 1.0 - p / 100.0;
    double pt = pow(p, t - 1);
    for (int j = 1; j <= T; j++) {
      double Tem = dp[i][j - 1];
      if (j - 1 >= t) {
        Tem -= dp[i - 1][j - 1 - t] * pt;
      }
      Tem *= p;
      if (j >= t) {
        Tem += dp[i - 1][j - t] * pt * p;
      }
      Tem += dp[i - 1][j - 1] * (1.0 - p);
      dp[i][j] = Tem;
      ans += Tem;
    }
  }
  printf("%.9f", ans);
  return 0;
}
