#include <stdio.h>
#include <string.h>
int main(void){
    int n,a,b,c;
    char x[1000000];
    while(~scanf("%d",&n)){
        memset(x,0,sizeof(x));
        for(a=2,c=0;a<=n;a++){
            if(x[a])continue;
            c++;
            for(b=a*2;b<=n;b+=a)x[b]=1;
        }
        printf("%d\n",c);
    }
    return 0;
}