#include <bits/stdc++.h>
using namespace std;
const int maxn = 5e3 + 10;
const int maxm = (1 << 19) + 10;
const long long inf = 1e18;
const long long mod = 1e9 + 7;
long long gcd(long long a, long long b) {
  while (a && b) {
    if (a >= b)
      a %= b;
    else
      b %= a;
  }
  return a + b;
}
long long power(long long a, long long n) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
    }
    n >>= 1;
    a *= a;
  }
  return p;
}
long long power(long long a, long long n, long long mod) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
      p %= mod;
    }
    n >>= 1;
    a *= a;
    a %= mod;
  }
  return p % mod;
}
int getint() {
  char c;
  while ((c = getchar()) && !(c >= '0' && c <= '9') && c != '-')
    ;
  int ret = c - '0', sgn = 0;
  if (c == '-') sgn = 1, ret = 0;
  while ((c = getchar()) && c >= '0' && c <= '9') ret = ret * 10 + c - '0';
  if (sgn) ret = -ret;
  return ret;
}
double dp[maxn][maxn];
double p[maxn];
int t[maxn];
double xpow(double x, int k) {
  double res = 1.0;
  while (k) {
    if (k & 1) res = res * x;
    x = x * x;
    k >>= 1;
  }
  return res;
}
int sum[maxn];
int main() {
  int n = getint(), T = getint();
  sum[0] = 0;
  for (int i = 1; i <= n; i++) {
    int x;
    scanf("%d", &x);
    scanf("%d", &t[i]);
    sum[i] = sum[i - 1] + t[i];
    p[i] = (double)x / 100;
  }
  double ans = 0;
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    dp[i][0] = 0;
    double t2 = xpow(1 - p[i], t[i]);
    for (int j = 1; j <= T; j++) {
      if (j > sum[i]) break;
      double res = dp[i][j - 1] * (1 - p[i]) + p[i] * dp[i - 1][j - 1];
      double temp = 0;
      if (j >= t[i] + 1) temp = dp[i - 1][j - t[i] - 1];
      if (j < t[i])
        dp[i][j] = res;
      else if (j >= t[i])
        dp[i][j] = res + dp[i - 1][j - t[i]] * t2 - temp * t2;
      ans += dp[i][j];
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
