#include <stdio.h>
#include <stdlib.h>

int prim[2000005];

int main(){
	FILE *fin = fopen("ciur.in", "r");
	FILE *fout = fopen("ciur.out", "w");
	int i, j, N, ans = 0;

	fscanf(fin, "%d", &N);

	for(i = 2; i <= N; i++)
		if(prim[i] == 0){
			ans++;
			for(j = i + i; j <= N; j = j + i)
				prim[j] = 1;
		}

	fprintf(fout, "%d", ans);

	fclose(fin);
	fclose(fout);
}