#include<cstdio>

using namespace std;
int n,c,i,j;
char p[2000010];

int main ()
{

	FILE *r = fopen("ciur.in", "r");
	FILE *w = fopen("ciur.out", "w");
	fscanf(r, "%d", &n);
	for(i=2;i*i<=n;i++)
        if(p[i]==0)
	    {
	        c++;
	        for(j=i*i;j<=n;j+=i)p[j]=1;
	    }
	for(;i<=n;i++)
        if(p[i]==0)c++;
	fprintf(w, "%d",c);
	return 0;
}