#include <cstdio>
using namespace std;

char ciur[2000000];

int main()
{
    FILE *f=fopen("ciur.in","r");
    int n,nc,i,np=0;
    fscanf(f,"%d",&n);
    fclose(f);
    ciur[1]=1;
    nc=2;
    while(1)
    {
        while(ciur[nc]&&nc<=n)nc++;
        if(nc>n)break;
        i=2;
        while(i*nc<=n)ciur[(i++)*nc]=1;
        np++;
        nc++;
    }
    f=fopen("ciur.out","w");
    fprintf(f,"%d",np);
    return 0;
}