#include "stdio.h"
#include "malloc.h"

using namespace std;

int main()
{
    int *v,n,i,nr(0),j;

    FILE* f=fopen("ciur.in","r");
    FILE* g=fopen("ciur.out","w");

    fscanf(f,"%i",&n);

    v=(int *)malloc(sizeof(int)*n);

    for(i=2;i<=n;i++)
        v[i]=0;

    for(i=2;i<=n;i++)
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+i)
                v[j]=1;

    for(i=2;i<=n;i++)
        if(v[i]==0)
            nr++;


    fprintf(g,"%i",nr);

    fclose(f);
    fclose(g);

    return 0;
}