#include <stdio.h>
#include <stdlib.h>

int ciur[2000000];
int main()
{
    FILE *f1,*f2;
    int n,i,j,c=0;

    f1=fopen("ciur.in","r");
    f2=fopen("ciur.out","w");
    fscanf(f1,"%d",&n);
    for(i=2;i<=n;i++){
		if(!ciur[i]){
			c++;
			for(j=i+i;j<=n;j+=i)
                ciur[j]=1;
            }
    }
    fprintf(f2,"%d\n",c);
    fclose(f1);
    fclose(f2);
}