#include <stdio.h>

bool s[2000001];
int n, i, j, nr;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for ( i = 2; i <= n; i++ )
        if ( s[i] == false )
        {
            nr++;
            for ( j = i; j <= n/i; j++ )
                s[i*j] = true;
        }
    printf("%d\n", nr);
    
    return 0;
}