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

int PrimeNumbersSieve4(int N){

int i, j, primes = 1;
char list[2000005]; memset(list, 0, 2000005);

for(i = 1; ((i * i) << 1) + (i << 1) <= N; i += 1){
    if(list[i] == 0){
        for(j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= N; j += (i << 1) + 1){
             list[j] = 1;
        }
    }
}
for (i = 1; 2 * i + 1 <= N; ++i){
    if(list[i] == 0){
        primes++;
    }
}
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", PrimeNumbersSieve4(N));

return 0;
}