#include <cstdio>
int main(){
    int N,M,P,Q,month;
    scanf("%d %d %d %d",&N,&M,&P,&Q);
    for(month=0;N>0;month++){
        N-=M;
        if(P<=month%12+1 && month%12+1<=P+Q-1)N-=M;
    }
    printf("%d\n",month);
    return 0;
}