#include <stdio.h>

int main(){

FILE *file1, *file2;
int N, i, j, primes = 1;
char list[2000005];

memset(list, 1, 2000005);

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

fscanf(file1, "%d", &N);

for(i = 3; i <= N; i+=2){
    if(list[i]){
        ++primes;
        for(j = i+i+i; j <= N; j += i<<1){
            list[j] = 0;
        }
    }
}

fprintf(file2, "%d", primes);

return 0;
}