#include <bits/stdc++.h>
using namespace std;
const int maxn = 5010;
double dp[maxn][maxn], p[maxn];
int t[maxn], n, T;
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    cin >> p[i] >> t[i];
    p[i] *= 0.01;
  }
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    double P = pow(1 - p[i], t[i]), tmp = 0;
    for (int j = i; j <= T; j++) {
      tmp += dp[i - 1][j - 1];
      if (j - t[i] - 1 >= 0) tmp -= dp[i - 1][j - t[i] - 1] * P;
      dp[i][j] = tmp * p[i];
      if (j - t[i] >= 0) dp[i][j] += dp[i - 1][j - t[i]] * P;
      tmp *= (1 - p[i]);
      ans += dp[i][j];
    }
  }
  printf("%.6f\n", ans);
}
