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

using namespace std;

char v[2000001];

int main()
{
    FILE *fin, *fout;
    int n,i,k,p;

    fin=fopen("ciur.in","r");
    fscanf(fin,"%d",&n);
    fclose(fin);

    p=0;
    for(k=2;k<=n;k++){
        if(v[k]==0){
            p++;
            for(i=k;i*k<=n;i++){
                v[i*k]=1;
            }
        }
    }

    fout=fopen("ciur.out","w");
    fprintf(fout,"%d",p);
    fclose(fout);
    return 0;
}