#include<stdio.h>
using namespace std;
FILE *f1=fopen("ciur.in","r");
FILE *f2=fopen("ciur.out","w");
int N,i,nr,v[2000005];
void erat(){
    int i,j;
    for (i=4;i<=N;i+=2)
        v[i]=1;
    nr=1;
    i=3;
    while(i<=N){
        if (v[i]==0)
        {
            nr++;
           j=i*i;
           while(j<=N){
              v[j]=1;
              j=j+i;
           }
         }
         i=i+2;
    }
}
int main(){
    fscanf(f1,"%d",&N);
    fclose(f1);
    erat();
    fprintf(f2,"%d",nr);
    fclose(f2);
    return 0;
}