#include <bits/stdc++.h>
using namespace std;
const int maxn = 5010;
int n, T;
double p[maxn];
int t[maxn];
double dp[maxn][maxn], Ans;
void Work() {
  dp[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    double f = 0, r = pow(1. - p[i], t[i] - 1);
    for (int j = 1; j <= T; j++) {
      f = f * (1. - p[i]) + dp[i - 1][j - 1];
      if (j >= t[i]) {
        f -= dp[i - 1][j - t[i]] * r;
        dp[i][j] = f * p[i] + dp[i - 1][j - t[i]] * r;
      } else
        dp[i][j] = f * p[i];
      Ans += dp[i][j];
    }
  }
  printf("%.10lf\n", Ans);
}
void Init() {
  scanf("%d%d", &n, &T);
  for (int i = 1; i <= n; i++) scanf("%lf%d", &p[i], &t[i]), p[i] /= 100;
}
int main() {
  Init();
  Work();
  return 0;
}
