#include <stdio.h>

int N, c;
char a[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++)
		if (!a[i]) {
			++c;
			for (j = i+i; j<=N; j+=i)
				a[j]=1;
		}
   
    printf("%d\n", c);

    return 0;
}