#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:1024000000,1024000000")
using namespace std;
double dp[2][5010], p[5010];
int n, T, t[5010];
int main() {
  int i, j, k, ca = 0, m;
  while (~scanf("%d%d", &n, &T)) {
    for (i = 0; i < n; i++) scanf("%lf%d", &p[i], &t[i]), p[i] /= 100;
    for (i = 0; i <= T + 5; i++) dp[0][i] = dp[1][i] = 0;
    int now = 0;
    T--;
    for (i = n - 1; i >= 0; i--, now = 1 - now) {
      double q = 1;
      for (j = 1; j < t[i]; j++) q *= (1 - p[i]);
      for (j = T; j >= 0; j--) {
        dp[1 - now][j] = (1 + dp[now][j + 1]) * p[i];
        double cur = dp[1 - now][j + 1];
        if (j + t[i] <= T) cur -= q * (1 + dp[now][j + t[i] + 1]);
        dp[1 - now][j] += cur * (1 - p[i]);
        if (j + t[i] - 1 <= T)
          dp[1 - now][j] -= q * p[i] * (1 + dp[now][j + t[i]]),
              dp[1 - now][j] += q * (1 + dp[now][j + t[i]]);
      }
    }
    printf("%lf\n", dp[now][0]);
  }
}
