#include <cstdio>

#define MIN(a,b) ((a<b) ? (a) : (b))

int main()
{
	FILE *in=fopen("fact.in", "r"), *out=fopen("fact.out", "w");
	int cifrez=0, nr=1, cinci=0, doi=0, aux;
	fscanf(in, "%d", &cifrez);
	while (cifrez>MIN(cinci, doi))
	{
		nr++;
		for (aux=nr; !(aux%2); doi++, aux/=2);
		for (; !(aux%5); cinci++, aux/=5);
	}
	fprintf(out, "%d", nr);
}