#include<stdio.h>

bool a[2000010];

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

    int n,c=0;
    fscanf(fin,"%d",&n);

    for(int i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            c++;
            for(int j=2;j*i<=n;j++)
            {
                a[i*j]=1;
            }
        }
    }
    fprintf(fout,"%d",c);
}