#include <bits/stdc++.h>
using namespace std;
const int MAX = 5010, MAXP = 101;
int ti[MAX], p[MAX];
double dp[MAX][MAX], memo[MAXP][MAX], pc[MAX];
double power(int pro, int x) {
  if (memo[pro][x] == -1) {
    memo[pro][x] = pow(double(pro) / 100, double(x));
  }
  return memo[pro][x];
}
int main() {
  int n, t;
  scanf("%d%d", &n, &t);
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &p[i], &ti[i]);
    pc[i] = double(p[i]) / 100.0;
  }
  for (int i = 0; i <= t; i++) {
    dp[n][i] = 0;
    for (int j = 0; j < MAXP; j++) {
      memo[j][i] = -1;
    }
  }
  for (int i = 0; i <= n; i++) dp[i][0] = 0;
  for (int i = n - 1; i >= 0; i--) {
    int l = 0, r = 0;
    double sol = dp[i + 1][0] + 1;
    for (int j = 1; j <= t; j++) {
      if (ti[i] != 1) {
        while (r < j - 1) {
          sol *= 1.0 - pc[i];
          sol += dp[i + 1][++r] + 1;
        }
        while (l < j - ti[i] + 1) {
          sol -= power(100 - p[i], r - l) * (dp[i + 1][l] + 1);
          l++;
        }
        dp[i][j] =
            sol * pc[i] + ((j - ti[i] >= 0) ? (1 + dp[i + 1][j - ti[i]]) *
                                                  power(100 - p[i], r - l + 1)
                                            : 0);
      } else {
        dp[i][j] = 1 + dp[i + 1][j - ti[i]];
      }
    }
  }
  printf("%.10lf\n", dp[0][t]);
  return 0;
}
