#include <stdio.h>

int ciur_eratostene (int numar) {
    int prime = 0;
    int prim[numar];
    int i, j;

    for (i = 2; i <= numar; i++)
        prim[i] = 1;
    for (i = 2; i <= numar; i++) {
        if (prim[i]) {
            prime++;
            j = 2 * i;
            while (j <= numar) {
                prim[j] = 0;
                j += i;
            }
        }
    }  
    return prime;
}

int main () {
	int numar;

    FILE *f_in = fopen("ciur.in", "r");
    FILE *f_out = fopen("ciur.out", "w");

    fscanf(f_in, "%d", &numar);
    int prime = ciur_eratostene(numar);
    fprintf(f_out, "%d\n", prime);
    
    return 0;
}