10200.cpp

#include <bits/stdc++.h>
using namespace std;

bool prime(long n) {
    long i;
    if (n == 2)
        return 0;
    else if (n % 2 == 0)
        return 1;
    for (i = 3; i * i <= n; i++)
        if (n % i == 0) return 1;

    return 0;
}

int main() {
    long long k, i;
    int b, c;
    double avg;
    int a[10002];
    a[0] = 0;
    a[1] = 1;
    for (i = 1; i <= 10000; i++) {
        k = (i * i) + i + 41;
        if (!prime(k))
            a[i + 1] = a[i] + 1;
        else
            a[i + 1] = a[i];
    }
    while (scanf("%d %d", &b, &c) == 2) {
        k = a[c + 1] - a[b];
        i = c - b + 1;
        avg = ((k / (double)i) * 100.0) + .0000000001;
        printf("%.2lf\n", avg);
    }
    return 0;
}