#include <stdio.h>
#include <string.h>

int PrimeNumbersSieve1(int N){

int i, j, primes = 0;
char list[2000005]; memset(list, 0, 2000005);

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

return primes;
}

int main(){

FILE *file1, *file2;
int N;

file1 = fopen("ciur.in", "r");
file2 = fopen("ciur.out", "w");

fscanf(file1, "%d", &N);
fprintf(file2, "%d", PrimeNumbersSieve1(N));

return 0;
}