#include <bits/stdc++.h>
using namespace std;
int n, T;
int p[5005], t[5005];
double dp[5005][5005];
double ans;
int main() {
  cin >> n >> T;
  for (int i = 0; i < n; i++) cin >> p[i] >> t[i];
  dp[0][0] = 1;
  for (int i = 0; i < n; i++) {
    double pro = p[i] * 0.01;
    double now = 0;
    double r = pow(1 - pro, t[i] - 1);
    for (int j = 0; j < T; j++) {
      now *= (1 - pro);
      now += dp[i][j] * pro;
      if (j + 1 >= t[i]) {
        now -= dp[i][j + 1 - t[i]] * r * pro;
        dp[i + 1][j + 1] = now + dp[i][j + 1 - t[i]] * r;
      } else
        dp[i + 1][j + 1] = now;
    }
    for (int j = 1; j <= T; j++) ans += dp[i + 1][j];
  }
  printf("%.1000f\n", ans);
  return 0;
}
