#include <iostream>
#include <stdio.h>
#define NMax 2000001
#define NMax1 1000000
using namespace std;
bool V[NMax]={0};

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int N,sol=0;
    V[0]=V[1]=1;
    for(int i=2;i<=NMax1;i++)
        if(!V[i])
        {
            for(int j=i*2;j<=NMax-1;j=j+i)
                V[j]=1;
        }
    scanf("%d",&N);
    for(int i=2;i<=N;i++)
        if(V[i]==0)
        sol++;
    printf("%d",sol);

}