//Maxim Daniel-Gabriel Gr: 135
#include <stdio.h>
#include <bitset>

using namespace std;

int main()
{
    unsigned int i,j,n,s=0;
    FILE *f=fopen("ciur.in","r");
    fscanf(f,"%d",&n);
    fclose(f);
    bitset <2000001> prim;
    for(i=2;i<=n;i++)
        if(prim.test(i)==0)
        {
            s++;
            for(j=2*i;j<=n;j+=i)
                prim.set(j,1);
        }
    f=fopen("ciur.out","w");
    fprintf(f,"%d",s);
    fclose(f);
    return 0;
}