#include <bits/stdc++.h>
using namespace std;
double dp[5005][5005], s[2][5005];
double fa[5005];
struct pi {
  int a;
  double p;
} pp[5005];
int main() {
  int i, j, n, m;
  cin >> n >> m;
  for (i = 1; i <= n; i++) {
    scanf("%d%d", &j, &pp[i].a);
    pp[i].p = j * 1.0 / 100;
  }
  for (i = 0; i == 0; i++) {
    for (j = 0; j <= m; j++) dp[i][j] = 0;
  }
  dp[0][0] = 1;
  int u = 0;
  s[0][0] = 1;
  for (i = 1; i <= m; i++) {
    s[0][i] = s[0][i - 1] * (1 - pp[1].p);
  }
  for (i = 1; i <= n; i++) {
    fa[i] = 1;
    for (j = 1; j <= pp[i].a - 1; j++) fa[i] = fa[i] * (1 - pp[i].p);
  }
  double ss = 0;
  for (i = 1; i <= n; i++) {
    u = u ^ 1;
    s[u][0] = 0;
    dp[i][0] = 0;
    for (j = 1; j <= m; j++) {
      dp[i][j] = 0;
      if (j >= pp[i].a) {
        dp[i][j] = (s[u ^ 1][j - 1] - s[u ^ 1][j - pp[i].a] * fa[i]) * pp[i].p;
        dp[i][j] += dp[i - 1][j - pp[i].a] * fa[i];
      } else {
        dp[i][j] = (s[u ^ 1][j - 1]) * pp[i].p;
      }
      s[u][j] = s[u][j - 1] * (1 - pp[i + 1].p) + dp[i][j];
      ss += dp[i][j];
    }
  }
  printf("%.9lf\n", ss);
}
