#include<fstream.h>
#include<string.h>

bool ok[2000000];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, j, i, p = 0;
    fin >> n;
    for(i = 0; i < n; i++)
        ok[i] = true;
    for(i = 2; i*i < n; i++)
        if ( ok[i] )
        {
            j = 2;
            while (i * j <= n)
            {
                ok [i*j] = false;
                j++;
            }
        }
        for (i = 2; i <= n; i++)
                if( ok[i] )
                p++;
    fout << p;
                
    fout << '\n';
    fin.close();
    fout.close();
    
    return 0;
}