#include <bits/stdc++.h>
using namespace std;
const int maxn = 5005;
inline int read() {
  char c = getchar();
  int t = 0, f = 1;
  while ((!isdigit(c)) && (c != EOF)) {
    if (c == '-') f = -1;
    c = getchar();
  }
  while ((isdigit(c)) && (c != EOF)) {
    t = (t << 3) + (t << 1) + (c ^ 48);
    c = getchar();
  }
  return t * f;
}
int n, T;
double p[maxn], dp[maxn][maxn];
int t[maxn];
int main() {
  n = read(), T = read();
  for (int i = 1; i <= n; i++) {
    p[i] = read(), t[i] = read();
    p[i] /= 100;
  }
  dp[0][0] = 1;
  double sum = 0;
  for (int i = 1; i <= n; i++) {
    double ans = 0, tp = pow(1 - p[i], t[i]);
    for (int j = i; j <= T; j++) {
      ans += dp[i - 1][j - 1];
      if (j - t[i] >= 1) ans -= dp[i - 1][j - t[i] - 1] * tp;
      dp[i][j] = ans * p[i];
      if (j - t[i] >= 0) dp[i][j] += dp[i - 1][j - t[i]] * tp;
      ans *= 1 - p[i];
      sum += dp[i][j];
    }
  }
  printf("%.9lf\n", sum);
  return 0;
}
