#include <bits/stdc++.h>
using namespace std;
const int N = 5e3 + 9;
int n, T;
int t[N];
double p[N], q[N], dp[2][N], s[2][N];
double power(double a, int b) {
  double r = 1;
  while (b > 0) {
    if (b & 1) r = r * a;
    a = a * a;
    b >>= 1;
  }
  return r;
}
int c(int i) { return i & 1; }
int o(int i) { return i & 1 ^ 1; }
int main() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; ++i) {
    int x;
    scanf("%d%d", &x, &t[i]);
    p[i] = x / 100.0;
    q[i] = (100.0 - x) / 100;
  }
  dp[0][0] = dp[1][0] = 0;
  s[0][0] = s[1][0] = 1;
  double sq = 1;
  for (int j = 1; j < t[n]; ++j) {
    sq *= q[n];
    dp[c(n)][j] = 1 - sq;
  }
  for (int j = t[n]; j <= T; ++j) dp[c(n)][j] = 1;
  for (int j = 1; j <= T; ++j) {
    s[c(n)][j] = s[c(n)][j - 1] * q[n - 1] + dp[c(n)][j] + 1;
  }
  for (int i = n - 1; i >= 1; --i) {
    for (int j = 1; j < t[i]; ++j) {
      dp[c(i)][j] = s[o(i)][j - 1] * p[i];
    }
    double tp = power(q[i], (t[i] - 1));
    for (int j = t[i]; j <= T; ++j) {
      dp[c(i)][j] = (s[o(i)][j - 1] - s[o(i)][j - t[i]] * tp) * p[i] +
                    tp * (dp[o(i)][j - t[i]] + 1);
    }
    for (int j = 1; j <= T; ++j) {
      s[c(i)][j] = s[c(i)][j - 1] * q[i - 1] + dp[c(i)][j] + 1;
    }
  }
  printf("%.9f\n", dp[1 & 1][T]);
  return 0;
}
