#include <bits/stdc++.h>
const int N = 5010;
inline int read() {
  int x = 0;
  char ch = getchar();
  while (!isdigit(ch)) ch = getchar();
  while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
  return x;
}
int t[N];
double p[N], f[N][N];
int main() {
  int n = read(), T = read();
  for (int i = 1; i <= n; ++i) scanf("%lf %d", &p[i], &t[i]), p[i] /= 100.0;
  f[0][0] = 1;
  double ans = 0;
  for (int i = 1; i <= n; ++i) {
    double sum = 0, tmp = pow(1 - p[i], t[i] - 1);
    for (int j = 1; j <= T; ++j) {
      (sum *= 1 - p[i]) += f[i - 1][j - 1] * p[i];
      if (j >= t[i])
        sum -= f[i - 1][j - t[i]] * tmp * p[i],
            f[i][j] += f[i - 1][j - t[i]] * tmp;
      ans += (f[i][j] += sum);
    }
  }
  std::cout << std::fixed << std::setprecision(7) << ans << std::endl;
  return 0;
}
