#include <stdio.h>

char v[20000000];

int main() {
    int n, i, j, count = 0;
    FILE* input = fopen("ciur.in", "r");
    FILE* output = fopen("ciur.out", "w");
    fscanf(input, "%d", &n);

    for (i = 2; i <= n; i++) {
        if (v[i] == 0) {
            count++;
            for (j = i * i; j <= n; j += i) {
                v[j] = 1;
            }
        }
    }
    
    fprintf(output, "%d", count);

    fclose(input);
    fclose(output);

    return 0;
}