#include <stdio.h>
#include <stdlib.h>
char c[2000001];

int main()
{
    FILE *in,*out;
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");
    int N, Nr = 0, i, j, x;
    fscanf(in,"%d",&N);
    for (i=2; i*i<=N; i++)
    {
        if(c[i]==0)
            for (j=i*i; j<=N; j=j+i)
                c[j]=1;
    }
    for(i=2; i<=N; i++)
        if (c[i]==0)
            Nr++;

    fprintf(out,"%d", Nr);
    return 0;
}