#include <stdio.h>

int main(void)
{
	int N, i, j, cnt;
	char prim[2000005];
	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;
}