#include<iostream.h>
#include<stdio.h>
#include<math.h>
int main(){


FILE *f = fopen ("fact.in","r");
FILE *g = fopen ("fact.out","w");

int p,i,m;
fscanf(f,"%d",&p);

long long a=0,b=100000000,c;
c=(a+b)/2;

while(1){
	for(i=5;i<=c;i+5){
		if(c%5==0){
			m++;
	              }
		else
			break;
	
		}
	if(m<p){
		a=c+1;
		}
	if(m>p){
		b=c-1;
		}
	if(m==p){
		break;
                }
       }
fprintf(g,"%ll",m);



fclose(f);
fclose(g);
return 0;
}