#include <bits/stdc++.h>
using namespace std;
const int N = 5000 + 7;
const int inf = 0x3f3f3f3f;
const long long INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);
int n, T, t[N];
double dp[N][N], p[N], q[N], f[N];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &p[i], &t[i]);
    p[i] /= 100;
    q[i] = 1 - p[i];
    f[i] = pow(q[i], t[i]);
  }
  double ans = 0;
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double gg = 0;
    for (int j = 1; j <= T; j++) {
      if (j < t[i]) {
        gg = gg * q[i] + p[i] * dp[i - 1][j - 1];
      } else if (j == t[i]) {
        gg = gg * q[i] + p[i] * dp[i - 1][j - 1] + f[i] * dp[i - 1][j - t[i]];
      } else {
        gg = gg * q[i] + p[i] * dp[i - 1][j - 1] -
             f[i] * dp[i - 1][j - t[i] - 1] + f[i] * dp[i - 1][j - t[i]];
      }
      dp[i][j] = gg;
      ans += dp[i][j];
    }
  }
  printf("%.12f\n", ans);
  return 0;
}
