#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
int t[N];
double dp[N][N], p[N];
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100.0;
  }
  dp[0][0] = 1;
  double ans = 0.0;
  for (int i = 1; i <= n; i++) {
    double sum = 0;
    double q = pow(1 - p[i], 1.0 * t[i]);
    for (int j = i; j <= m; j++) {
      sum += dp[i - 1][j - 1];
      if (j - t[i] - 1 >= 0) sum -= dp[i - 1][j - t[i] - 1] * q;
      dp[i][j] = sum * p[i];
      if (j - t[i] >= 0) dp[i][j] += dp[i - 1][j - t[i]] * q;
      sum *= (1.0 - p[i]);
      ans += dp[i][j];
    }
  }
  printf("%.8lf\n", ans);
  return 0;
}
