#include <stdio.h>
#include <stdlib.h>
int c[2000000];

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

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