#include <stdio.h>
char ciur[2000000];

int main()
{
    FILE *fin, *fout;
    int n,i,d,rez=0;
    fin = fopen( "ciur.in", "r" );
    fout = fopen( "ciur.out", "w" );
    fscanf( fin, "%d", &n );
    ciur[0]=ciur[1]=1;
    for(i=2;i*i<=n;i++) {
        if(ciur[i]==0)
          for(d=i*i;d<=n;d+=i)
                ciur[d]=1;
    }
    for(i=2;i<=n;i++)
        if(ciur[i]==0)
            rez++;
    fprintf( fout,"%d",rez);
    fclose( fin );
    fclose( fout );
    return 0;
}