#include <stdio.h>
#include <stdlib.h>
char ciur[2000000];
int main()
{
    int n,i,c=0,j;
    FILE *fin=fopen("ciur.in","r");
    FILE *fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    //scanf("%d",&n);
    for(i=1; ((i<<1)+1)<=n; i++)
        if(ciur[(i<<1)+1]==0){
            c++;
            for(j=((i<<1)+1); j<=n; j+=((i<<1)+1)<<1)
                ciur[j]=1;
        }
    //printf("%d",c+1);
    fprintf(fout,"%d",c+1);

    return 0;
}