#include <stdio.h>
#include <stdlib.h>
#define MAX_NUM 999999
int numbers[MAX_NUM] = {-1, -1};
int isPrime(int num) {
    int i;
    if(numbers[num]) {
        return 0;
    }
    for(i=num << 1; i<=MAX_NUM; i+=num) {
        numbers[i] = -1;
    }
    return 1;
}

int main() {
    int i, n, count;
    while(scanf("%d", &n) != EOF){
        count = 0;
        for(i=2; i<=n; ++i) {
            count += isPrime(i);
        }
        printf("%d\n", count);
    }
    return 0;
}