#include <stdio.h>

int putere5(int n){
    int p5=5,t=0;

    while(p5<=n){
        t+=n/p5;
        p5*=5;
    }
    return t;
}

int main(){
    FILE *fin=fopen("fact.in","r");
    FILE *fout=fopen("fact.out","w");
    int p,i,pas;

    fscanf(fin,"%d",&p);
    i=0;
    pas=1<<30;
    while(pas!=0){
        if(putere5(i+pas)<p)
            i+=pas;
        pas/=2;
    }
    fprintf(fout,"%d\n",i+1);
    fclose(fin);
    fclose(fout);
    return 0;
}