#include <stdio.h>
using namespace std;
bool a[2000000];
int main()
{
    FILE*in = fopen("ciur.in", "r"); FILE*out = fopen("ciur.out", "w");

    int n, contor = 0;

    fscanf(in, "%d", &n);

    for ( int i = 2; i <= n; i++ ) {
        if ( a[i] == false )
            for ( int j = i*i; j <= n; j += i ) {
                a[j] = true;
                contor++;
            }
    }
    fprintf(out, "%d", contor-1);

    return 0;
}