uva884.c

uva884.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int primes[168] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53,
    59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137,
139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227,
229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313,
317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419,
421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509,
521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617,
619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727,
733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829,
839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947,
953, 967, 971, 977, 983, 991, 997};

int mpf[1000000+1];
int dp[1000000+1];

int main() {

    memset(mpf, 0, sizeof(mpf));
    int i, j;
    for(i=0; i<168; i++) {
        mpf[primes[i]] = primes[i];
        for(j=primes[i]*primes[i]; j <= 1000000; j+=primes[i])
            mpf[j] = primes[i];
    }
    
    dp[0] = 0;
    dp[1] = 0;
    dp[2] = 1;

    for(i=3; i<=1000000; i++) {
        int cnt = 0;
        int temp = i;
        while (temp != 1) {
            if (mpf[temp] == 0) {
                cnt += 1;
                break;
            }
            
            temp = temp / mpf[temp];
            cnt++;
        }
        
        dp[i] = dp[i-1] + cnt;
    }
    
    
    int query;
    while (scanf("%d", &query) != EOF) {
        printf("%d\n", dp[query]);
    }
    
    return 0;
}