#include <cstdio>
#include <cstdlib>

FILE *fin=fopen("ciur.in","r");
FILE *fout=fopen("ciur.out","w");

bool a[2000010];

int main (int argc, char * const argv[]) {
	int n,nr=0;
	fscanf(fin, "%d", &n);
	for (int i=2; i<=n; i++)
		if (!a[i])
		{
			nr++;
			for (int j=i<<1; j<=n; j+=i)
				a[j]=true;
		}
	fprintf(fout, "%d\n",nr);
	fclose(fin);
	fclose(fout);
    return 0;
}