#include <stdlib.h>
int scanf(const char *, ...);
int printf(const char *, ...);
int f(unsigned int n);

/* Количество простых чисел, меньших n
 */
int f(unsigned int n)
{
    unsigned int i, j, res = 0;
    char *a;

    a = (char *)malloc(n*sizeof(char));
    if(a==0) {
        free(a);
        return -1;
    }

    for(i = 0; i<n; i++) a[i] = 1;

    for(i = 2; i*i<n; i++)
    {
        if(a[i]==1)
            for(j = i; j<=(unsigned int)(n/i); j++) a[j*i] = 0;
    }

    //for(i = 0; i<n; i++) printf("%d\t%d\n", i, a[i]);

    for(i = 2; i<n; i++)
        res += a[i];

    free(a);
    return res;
}

int main(void)
{
    unsigned int n;

    printf("n=");
    if( scanf("%u", &n)==0 )
    {
        printf("Input error!\n");

        return 1;
    }

    printf("Result: %d\n", f(n));

    return 0;
}