#include <stdio.h>

int divByFive(int nr){
	int nrDiv = 0;
	while(nr % 5 == 0){
		nrDiv++;
		nr /= 5;
	}
	return nrDiv;
}
int main(){
	FILE *in, *out;
	int P, N = 0, count = 0;
	in = fopen("factorial.in", "r");
	out = fopen("factorial.out", "w");
	fscanf(in, "%d", &P);
	while(N < P){
		count++;
		if(count % 5 == 0){
			N += divByFive(count * 5);
		}
		else{
			N++;
		}
	}
	fprintf(out, "%d", count * 5);	
	return 0;
}