#include <stdio.h>
#define N 2000000
char ciur[N];
int main()
{
    FILE *f1 = fopen("ciur.in","r"), *f2 = fopen("ciur.out","w");
    int i, n, prim=0,j;
    fscanf(f1,"%d",&n);
    for(i=2;i<=n;i++){
        if(ciur[i]==0){
            prim++;
            for(j=i;j<=n;j=j+i)
                ciur[j]=1;
        }
    }
    fprintf(f2,"%d",prim);
    return 0;
}