#include <bits/stdc++.h>
using namespace std;
double dp[5005][5005];
int t[5005];
double p[5005];
double sum, bei, tmp;
int main() {
  int n, T;
  cin >> n >> T;
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
  }
  double ans = 0;
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double P = p[i], VP = 1 - p[i], VPN = pow(VP, t[i]);
    double temp = 0;
    for (int j = 0; j <= T; j++) {
      if (j >= 1) temp += dp[i - 1][j - 1];
      if (j >= t[i] + 1) temp -= dp[i - 1][j - t[i] - 1] * VPN;
      dp[i][j] += temp * P;
      if (j >= t[i]) dp[i][j] += dp[i - 1][j - t[i]] * VPN;
      temp = temp * VP;
      ans += dp[i][j];
    }
  }
  printf("%.11lf\n", ans);
}
