100%AC

#include<cstdio>
int run(int y){return(y%4==0&&y%100!=0||y%400==0)?true:false;}
int big(int m){return(m<=7&&m%2==1||m>=8&&m%2==0)?true:false;}
int main(){
    int y,m;
    scanf("%d %d",&y,&m);
    printf(m==2?(run(y)?"29":"28"):(big(m)?"31":"30"));
}