#include<cstdio>
#include<cstring>

char s[] = "0.1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
char ans[200];

int main(){
  int n;
  scanf("%d",&n);
  int res = 0;
  int p = 0;
  for(int i=2;i<192;i++){
    res = res+n*(s[i]-48);
    sprintf(ans+p,"%d",res/10000);
    p = strlen(ans);
    res%=10000;
    res*=10;
  }
  if(res<10){
    sprintf(ans+p,"0000");
    p+=4;
  }else if(res<100){
    sprintf(ans+p,"000");
    p+=3;
  }else if(res<1000){
    sprintf(ans+p,"00");
    p+=2;
  }else if(res<10000){
    sprintf(ans+p,"0");
    p++;
  }
  sprintf(ans+p,"%d",res);
  if(n<=8) printf("0");
  else if(n<=81) printf("%c",ans[3]);
  else printf("%c%c",ans[2],ans[3]);
  printf(".%s\n",ans+4);
}