#include <bits/stdc++.h>

using namespace std;

#define f first
#define s second

ifstream fin( "ciur.in" );
ofstream fout( "ciur.out" );

char v[2000010];
int i,j,n,m,ans;

int main()
{
    fin>>n;
    for( i = 2 ; i <= n ; i++ )
    {
        if( v[ i ] == 0 )
        {
            for( j = i + i ; j <= n ; j += i )
                v[ j ] = 1;
            ++ans;
        }
    }
    fout<<ans;

return 0;
}