#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const int inf = 1e9;
long long powm(long long a, long long p, long long m) {
  long long r = 1 % m;
  while (p) {
    if (p & 1) r = r * a % m;
    p >>= 1;
    a = a * a % m;
  }
  return r;
}
double dp[5001][5001];
int main() {
  int n, T, p, t;
  double ans = 0;
  scanf("%d%d", &n, &T);
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; ++i) {
    scanf("%d%d", &p, &t);
    double pp = p / 100.0, qq = pow(1 - pp, t - 1), sum = 0;
    for (int j = i; j <= T; ++j) {
      sum = sum * (1 - pp) + dp[i - 1][j - 1];
      if (j >= t) {
        sum -= qq * dp[i - 1][j - t];
        dp[i][j] = dp[i - 1][j - t] * qq;
      }
      dp[i][j] += sum * pp;
      ans += dp[i][j];
    }
  }
  printf("%0.9lf\n", ans);
  return 0;
}
