#include<stdio.h>

long  n,i,j,nr;
char a[2000001];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	for(i=2;i<=n;i++)
	    if (!a[i])
        {
            ++nr;      
        	j=2*i;
			while(j<=n)
			{
				a[j]=1;
                j+=i;
            }
		}



    printf("%ld",nr);
    return 0;
}