#include <stdio.h>

int N, cnt;
char prim[2000005];

int main()
{
    int i, j;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &N);
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i + i; j <= N; j += i)
                prim[j] = 0;
        }
    printf("%d", cnt);
    return 0;
}