#include <iostream>
#include <fstream>

using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
bool c[2000000];

int main()
{
    int i,j,n,s=0;
    fi>>n;
    fi.close();
    for(i=2;i*i<=n;i++)
        if(!c[i])
            for(j=i*i;j<=n;j+=i)
                c[j]=1;
    for(i=2;i<=n;i++)
        if(c[i]==0)
            s++;



    fo<<s;
    fo.close();

    return 0;
}