#include <stdio.h>
long int n,nr=0,i,j,prime[2000001];
FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
int main()
{
   fscanf(f,"%ld",&n);
    for(i=2; i<=n; i++){prime[i]=1;}
    for(i=2; i<=n; i++){
        if(prime[i]==1){
            nr++;
            for(j=i+i; j<=n; j=j+i){
                prime[j]=0;
            }
        }
    }
    fprintf(g,"%ld",nr);
    return 0;
}