#include<stdio.h>
#include<math.h>
#define MAX 2000005
int main(){

    FILE *fin=fopen("ciur.in","r");
    FILE *fout=fopen("ciur.out","w");

    int N,k=0;

    fscanf(fin,"%d",&N);

    unsigned char a[MAX];
    for(int i=1;i<=N;i++) a[i]=1;

    ++k;
    int i=2;
    for(int j=2;i*j<=N;j++) a[i*j]=0;

    for(i=3;i<=N;i+=2)
        if(a[i]==1){
            k++;
            for(int j=i;j*i<=N;j+=2) a[i*j]=0;
            }

    fprintf(fout,"%d\n",k);


    fclose(fin);
    fclose(fout);

    return 0;
    }