#include <cstdio>

unsigned int n,prim[2000000],max;

void ciur() { 
	int i,j;
	for(i=2; i<=n; i++) prim[i]=1;
	for(i=2; i<=n; i++)
		if(prim[i]){
			max++;
			for(j=i+i; j<=n; j+=i) {
				prim[j]=0;
			}
		}
}

int main() {
	FILE *f=fopen("ciur.in","r");
	FILE *g=fopen("ciur.out","w");
	fscanf(f,"%d",&n);
	ciur();
	fprintf(g,"%d",max);
	fclose(f);
	fclose(g);
	return 0;
}