#include <stdio.h>
#define MAX 2000010
#define MAXD 2000000
char ciur[MAX];
FILE *fin, *fout;
long long N, rasp;

int main()  {
    long long i, j;
    fin = fopen("ciur.in", "r");
    fscanf(fin, "%lld", &N);
    fclose(fin);
    fout = fopen("ciur.out", "w");
    for(i = 2;i <= MAXD;i++)
        if(ciur[i] == 0)
        for(j = i * i;j <= MAXD;j += i)
            ciur[j] = 1;
    for(i = 2;i <= N;i++)
        if(ciur[i] == 0)
            rasp++;
    fprintf(fout, "%lld", rasp);
    fclose(fout);
    return 0;
}