#include<stdio.h>

int n;

int main()
{
    FILE *fin, *fout;
    fin = fopen("ciur.in", "r");
    fout = fopen("ciur.out", "w");

    fscanf(fin, "%d", &n);
    bool marked[n+1];
    for (int i = 2 ; i <= n ; i++)
        marked[i] = 0;
    for(int i = 2; i*i <= n ; i++)
        if(marked[i] == 0)
            for(int j = i * i ; j <= n ; j = j + i)
                marked[j] = 1;
    int nr=0;
    for (int i = 2 ; i <= n ; i++)
        if (marked[i] == 0)
            nr++;
    fprintf( fout, "%d", nr);
    fclose(fin);
    fclose(fout);
}