#include<stdio.h>

int prim(int x)
{
    for(int i = 2; i*i <= x; i++)
        if(x%i==0)
            return 0;
    return 1;
}
int main(){
    FILE* in = fopen("ciur.in","r");
    FILE* out = fopen("ciur.out","w");
    
    int n,k=0;

    fscanf(in,"%d",&n);

    for(int i = 2; i <= n; i++ )
        if(prim(i))
            k++;
    fprintf(out,"%d",k);

    fclose(in);
    fclose(out);
    return 0;
}