#include<stdio.h>

int main(){
    int n, a, b,c,d;
    scanf("%d",&n);
    if(n<10){printf("%d",n);}
        else{
            a = n / 10;
            b = n % 10;
            c = b % 2;
            d = a % 2;
            if(c==0){ printf("%d",(a+1)/2);}
                else{
                    if(d==0){
                       if(b==1){printf("5");}
                       else if(b==3){printf("6");}
                       else if(b==5){printf("7");}
                       else if(b==7){printf("8");}
                       else {printf("9");}
                    }
                    else{printf("%d",b/2);}
                }
        }
}