#include <stdio.h>
#include <stdlib.h>
char ciur[2000001];
int main()
{
    FILE*fin,*fout;
    int n,i,j,nr=0;
    fin = fopen("ciur.in" ,"r");
    fout = fopen("ciur.out" ,"w");
    fscanf(fin, "%d" ,&n);
    for(i=2;i<=n;i++){
        if(ciur[i]==0){
            nr++;
            for(j=i*i;j<=n;j+=i)
                ciur[j]=1;
        }
    }
    fprintf(fout, "%d\n" ,nr);
    fclose(fin);
    fclose(fout);
    return 0;
}