#include<cstdio>
int n,i,j,v[2001000],nr;
FILE *f,*g;
int main(){
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    v[1]=1;
    for(i=2;i<=n;i++){
        if(v[i]==0){
            nr++;
            for(j=i+i;j<=n;j+=i){
                v[j]=1;
            }
        }
    }
    fprintf(g,"%d",nr);


    fclose(f);
    fclose(g);
    return 0;
}