#include<stdio.h>
#define MAXN 2000000
void ciur(int N);
FILE*fin,*fout;
bool marked[MAXN+1];
long long cnt=0;
int main()
{
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    int N;
    fscanf(fin,"%d",&N);
    ciur(N);
    fprintf(fout,"%lld",cnt);
    fclose(fin);
    fclose(fout);
}
void ciur(int N)
{
    marked[0]=1;
    marked[1]=1;
    for(int i=2;i<=N;i++)
    {
        if(!marked[i])
        {
            cnt++;
            for(int j=i*i;j<=N;j+=i)
            {
                marked[j]=1;
            }
        }
    }
}