#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5010;
long double dp[2][MAXN], p[MAXN], pw[MAXN], dp2[2][MAXN];
int x[MAXN];
int main() {
  int n, t;
  cin >> n >> t;
  for (int i = 0; i < n; i++) {
    cin >> p[i] >> x[i];
    p[i] /= 100.0;
  }
  dp[0][0] = 1;
  dp2[0][0] = 1;
  for (int j = 1; j < x[0]; j++) dp[0][j] = dp[0][j - 1] * (1 - p[0]);
  pw[0] = 1;
  for (int j = 0; j < x[0]; j++) pw[0] *= 1 - p[0];
  long double ans = 0, pr = 1 - dp[0][t];
  for (int i = 1; i < n; i++) {
    pw[i] = 1;
    dp[i % 2][0] = dp2[i % 2][0] = 0;
    for (int j = 1; j <= t; j++) {
      if (j <= x[i]) pw[i] *= 1 - p[i];
      dp2[i % 2][j] = dp[(i - 1) % 2][j - 1] * p[i - 1];
      if (j >= x[i - 1])
        dp2[i % 2][j] += dp2[(i - 1) % 2][j - x[i - 1]] * pw[i - 1];
      dp[i % 2][j] = dp[i % 2][j - 1] * (1 - p[i]) + dp2[i % 2][j];
      if (j >= x[i]) dp[i % 2][j] -= dp2[i % 2][j - x[i]] * pw[i];
    }
    ans += i * dp[i % 2][t];
    pr -= dp[i % 2][t];
  }
  ans += pr * n;
  cout.precision(9);
  cout << fixed << ans << endl;
}
