#include <bits/stdc++.h>
using namespace std;
double dp[2][5005];
int n, t;
void solve() {
  double ans = 0, pi;
  int cur = 0, ti;
  fill(dp[0], dp[2], 0);
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    scanf("%lf%d", &pi, &ti);
    pi /= 100.0;
    double q = pow(1 - pi, 1.0 * ti);
    cur ^= 1;
    double tmp = 0;
    for (int j = 0; j < i; j++) dp[cur][j] = 0;
    for (int j = i; j <= t; j++) {
      tmp += dp[cur ^ 1][j - 1];
      if (j - ti - 1 >= 0) tmp -= dp[cur ^ 1][j - ti - 1] * q;
      dp[cur][j] = tmp * pi;
      if (j - ti >= 0) dp[cur][j] += dp[cur ^ 1][j - ti] * q;
      tmp *= (1 - pi);
      ans += dp[cur][j];
    }
  }
  printf("%.6f\n", ans);
}
int main() {
  while (~scanf("%d%d", &n, &t)) solve();
  return 0;
}
