#include <cstdio>

#define N 2000000

int n, nr, prim[N];

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