#include <bits/stdc++.h>
using namespace std;
int INT_MAX_VAL = (int)1e20;
int INT_MIN_VAL = (int)-1e20;
long long LONG_MAX_VAL = (long long)1e20;
long long LONG_MIN_VAL = (long long)-1e20;
double dp[5005][5005];
double pow_(double a, int b) { return exp(log(a) * b); }
int main() {
  int n, T;
  scanf("%d%d", &n, &T);
  double p[5005];
  int t[5005];
  for (long long(i) = 0LL; (i) < (n); (i)++) {
    int u;
    scanf("%d%d", &u, &t[i]);
    p[i] = u * 0.01;
  }
  dp[0][0] = 1;
  for (int i = 0; i < n; ++i) {
    double cur = 0;
    double r = pow_(1 - p[i], t[i] - 2);
    for (int j = 0; j <= T; ++j) {
      if (p[i] == 1 || t[i] == 1) {
        dp[i + 1][j] = j ? dp[i][j - 1] : 0;
      } else {
        if (j) {
          if (j >= t[i]) {
            cur -= dp[i][j - t[i]] * p[i] * r;
          }
          cur = cur * (1 - p[i]) + dp[i][j - 1] * p[i];
        }
        dp[i + 1][j] = cur;
        if (j >= t[i]) {
          dp[i + 1][j] += r * (1 - p[i]) * dp[i][j - t[i]];
        }
      }
    }
  }
  double res = 0;
  for (long long(i) = 0LL; (i) < (n); (i)++)
    for (long long(j) = 0LL; (j) < (T + 1); (j)++) res += dp[i + 1][j];
  cout << setprecision(9) << fixed << res << '\n';
  return 0;
}
