#include <stdio.h>
#include <math.h>

const int range = 10;

int nrzerofact(int n){
    int maxim = 0;
    int copie = n;
    while(copie) {
        copie = copie/5;
        maxim++;
    }
    int suma=0;
    for(int i=1; i<maxim; i++){
        suma+=n/pow(5,i);
    }
    return suma;
}

int main() {
    FILE *in = fopen("fact.in", "r");
    FILE *out = fopen("fact.out", "w");
    int P, aux=1;
    fscanf(in, "%d", &P);
    int k=P/5-range;
    if(k<0)k=0;
    while(nrzerofact((P-k)*5)!=P){
        k++;
    }
    fprintf(out,"%d", (P-k)*5);
}