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#include <stdio.h>
#include <math.h>

int main(){
    //freopen("in.txt","r",stdin);
    double x1 = 0,x2 = 0,y1 = 0,y2 = 0;
    while(scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2)!=EOF){
        printf("%.2lf\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
    }
    return 0;
}