#include <bits/stdc++.h>
using namespace std;
int n, m;
double ans, p1;
double f[5005][5005];
double p[5005], tmp[5005];
int t[5005];
signed main() {
  scanf("%d%d", &n, &m);
  for (register int i = 1; i <= n; ++i) {
    int x;
    scanf("%d", &x);
    p[i] = x / 100.0;
    scanf("%d", &t[i]);
  }
  f[1][0] = 1;
  p[n + 1] = 0, t[n + 1] = 5000;
  for (register int i = 1; i <= n + 1; ++i) {
    p1 = pow(1 - p[i], t[i]);
    for (register int j = 0; j <= m; ++j) tmp[j] = f[i][j];
    for (register int j = 0; j <= m; ++j) {
      f[i][j + 1] += f[i][j] * (1 - p[i]);
      f[i + 1][j + 1] += f[i][j] * p[i];
      if (j + t[i] <= m) {
        f[i][j + t[i]] -= tmp[j] * p1;
        f[i + 1][j + t[i]] += tmp[j] * p1;
      }
    }
  }
  for (register int i = 1; i <= n + 1; ++i) ans += f[i][m] * (i - 1);
  printf("%.10lf", ans);
  return 0;
}
