#include <stdio.h>

int N, cnt;
bool prim[2000005];

int main(void)
{
    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\n", cnt);

    return 0;
}