#include <iostream>
#include <stdio.h>
#include<math.h>
using namespace std;
int A[2000001];
int main()
{
    int n,i,j;
    FILE *f=fopen("ciur.in","rt");
    FILE *g=fopen("ciur.out","wt");
    fscanf(f,"%d",&n);
    //scanf("%d",&n);
    for (i=2;i<=sqrt(n);i++)
        if (A[i]==0)
            for (j=i*i;j<=n;j=j+i)
                A[j]=1;
    int countt=0;
    for (i=2;i<=n;i++)
            if(A[i]==0)countt++;
    fprintf(g,"%d",countt);
    //printf("%d",countt);
    fclose(f);
    fclose(g);
    return 0;
}