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

bool c[2000000001];

int main()
{
    FILE *fin, *fout;
    fin=fopen("ciur.in", "r");
    fout=fopen("ciur.out", "w");
    int n, i, j, contor=0;
    fscanf(fin, "%d", &n);
    for(i=2; i*i<=n; i++)
    {
        if(!c[i])
        {
            for(j=i*i; j<=n; j+=i)
            {
                c[j]=true;
            }
        }
    }
    for(i=2; i<=n; i++)
    {
        if(!c[i])
        {
            contor++;
            //printf("%d ", i);
        }
    }
    fprintf(fout, "%d", contor);
    fclose(fin);
    fclose(fout);
    return 0;
}