#include <bits/stdc++.h>
using namespace std;
int n;
int T;
int tmp;
int t[5001];
double ans;
double p[5001];
double rate[5001];
double dp[5001][5001];
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &tmp, &t[i]);
    p[i] = tmp / 100.0;
  }
  dp[0][0] = 1.0;
  for (int i = 1; i <= n; i++) {
    double mul = 1.0;
    for (int j = 0; j < t[i]; j++) {
      dp[i][j + 1] = dp[i][j] * (1 - p[i]) + dp[i - 1][j] * p[i];
      mul *= (1 - p[i]);
    }
    dp[i][t[i]] += dp[i - 1][0] * mul;
    for (int j = t[i]; j < T; j++) {
      dp[i][j + 1] = dp[i][j] * (1 - p[i]) + dp[i - 1][j] * p[i];
      dp[i][j + 1] += (dp[i - 1][j - t[i] + 1] - dp[i - 1][j - t[i]]) * mul;
    }
  }
  fill(rate, rate + n + 1, 1.0);
  for (int i = 1; i < n; i++) {
    int lim = T - t[i + 1];
    for (int j = T; j > lim; j--) {
      ans += dp[i][j] * i * rate[i];
      rate[i] *= (1 - p[i + 1]);
    }
  }
  for (int j = T; j > 0; j--) {
    ans += dp[n][j] * n;
  }
  printf("%f\n", ans);
}
