#include <fstream>

using namespace std;

int p;

int putere(int n){
    int r=0;
    while(n>=1){
        r+=n/5;
        n/=5;
    }
    return r;
}
int cb(){
    int i,pas=1<<30;
    for(i=0;pas!=0;pas/=2)
        if(putere(i+pas)<p)i+=pas;
    return 1+i;
}
int main(){
    ifstream f("factorial.in");
    ofstream h("factorial.out");
    f>>p;
    h<<cb();
    return 0;
}