#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const double eps = 1e-6;
const int N = 5010;
int cas = 1;
int n, T, t[N];
double p[N], q[N], dp[2][N];
double pass[N];
void work() {
  dp[0][0] = 1.0;
  memset(pass, 0, sizeof(pass));
  int now = 0;
  for (int i = 1; i <= n; i++) {
    now ^= 1;
    dp[now][0] = 0;
    double qq = 1.0;
    for (int k = 1; k <= t[i]; k++) qq *= q[i];
    for (int j = 0; j < T; j++) {
      dp[now][j + 1] = dp[now][j] * q[i] + dp[!now][j] * p[i];
      if (j - t[i] >= 0) dp[now][j + 1] -= dp[!now][j - t[i]] * qq;
      if (j - t[i] + 1 >= 0) dp[now][j + 1] += dp[!now][j - t[i] + 1] * qq;
      pass[i] += dp[now][j + 1];
    }
  }
}
void run() {
  memset(dp, 0, sizeof(dp));
  int i, j, k;
  for (i = 1; i <= (n); i++) {
    cin >> p[i] >> t[i];
    p[i] /= 100;
    q[i] = 1 - p[i];
  }
  work();
  double ans = 0.0;
  for (i = 1; i <= n; i++) ans += i * (pass[i] - pass[i + 1]);
  printf("%.9f\n", ans);
}
int main() {
  while (cin >> n >> T) run();
  return 0;
}
