#include <stdio.h>

int main(void)
{
	int N, nr = 0;
    
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &N);
    int A[N];

    for(int i = 2; i <= N; i++){
        A[i] = 1; // initialy is true
    }

    for(int i = 0; i < N; i++){
    	if(A[i] == 1){
            nr++;
            for(int j = i*i; j <= N; j += i){
                A[j] = 0;
            }
        }

    }

    printf("%d", nr);
    //printf("\n");

    return 0;

}