#include <bits/stdc++.h>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool ciur[2000005];

int main()
{
    int i,j,n,sol=0;
    f>>n;
    ciur[0]=ciur[1]=1;
    for(i=4;i<=2000000;i+=2)ciur[i]=1;

    for(i=3;i*i<=2000000;i+=2)
        if(ciur[i]==0)
        {
            for(j=i*i;j<=2000000;j+=i)ciur[j]=1;
        }
    for(i=2;i<=n;i++)if(ciur[i]==0)sol++;
        g<<sol;
    return 0;
}