#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
    FILE* in = fopen("ciur.in", "r");
    FILE* out = fopen("ciur.out", "w");
    int n;
    fscanf(in, "%d", &n);
    int* array = (int*)malloc(sizeof(int) * (n + 1));
    memset(array, 0, sizeof(int) * (n + 1));

    int ct = 0;
    for(int i = 2; i <= n; i++)
    {
        if(!array[i]) {

            ct++;
            for(int j = i * 2; j <= n; j += i)
            array[j] = 1;
    }
        }



    fprintf(out, "%d", ct);
    return 0;
}