#include <bits/stdc++.h>
using namespace std;
const int maxn = 5100;
int n, m, a[maxn];
double f[maxn][maxn], p[maxn], ans;
int main() {
  scanf("%d%d", &n, &m);
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    scanf("%lf%d", &p[i], &a[i]);
    p[i] /= 100;
    double sum = 0, mi = pow(1 - p[i], a[i] - 1);
    for (int j = 1; j <= m; ++j) {
      sum *= (1 - p[i]);
      sum += f[i - 1][j - 1] * p[i];
      if (j >= a[i]) {
        sum -= f[i - 1][j - a[i]] * mi * p[i];
        f[i][j] += f[i - 1][j - a[i]] * mi;
      }
      f[i][j] += sum;
      ans += f[i][j];
    }
  }
  printf("%.9lf\n", ans);
  return 0;
}
