#include<stdio.h>
#include<vector>
using namespace std;
FILE *in=fopen("ciur.in","rt");
FILE *out=fopen("ciur.out","wt");
int j,i,n,cont;
vector <bool> prim;
int main()
{
    fscanf(in,"%d",&n);
    prim.resize(n,true);
    for(i=2;i<=n;i++)
        if(prim[i]==true)
        {
            cont++;
            for(j=i*2;j<=n;j+=i)
                prim[j]=false;
        }

    fprintf(out,"%d",cont);
    return 0;
}